Plagiarism is the art of representing the work of another as your own. Successful plagiarism may be described, then, as plagiarism where you succeed in presenting the work of the other, and are never yourself found out to have done so. Don't get caught, folks, that is the mantra. The march of technological detection has progressed so that it is now possible with fairly shocking ease for an educator who has assigned a writing task to students (who are most likely in need of this art) to check the originality of their work against most anything that has ever been written, should such writing somehow make it to the Internet (including, by the way, through another educator having similarly uploaded past student papers in a similar search). Which means that if you seriously desire to plagiarize like the dickens and not to be caught, you've got essentially two options left before you. One is to plagiarize work which has nowhere else ever seen the light of electrons carrying it through wires (or even, now, through the aether) to a computer. Dig through that old shoebox in the attic where your dad keeps his college memorabilia and see what you can find of his writings from those swell old knockabout days, for example. But the chances are slim that you'll find anything germane to whatever you have been or may ever be required to write by assignment.

On to method two -- word shifting. This is where you actually put a bit of elbow grease into your intellectual larceny, and it's quite a bit harder than it sounds, but with a bit of practice becomes a delightful art form. Find something someone else has written and through a combination of substitution of appropriate synonyms for words used by the original author and a dash of grammatical license, make it barely recognizable as a derivation of that original. Care must be taken in both actions, else the end result of your labors will be turning a passable essay into a word salad of the intellectually inedible variety.

So, to begin, here is a passage on freedom which I have more or less randomly copped from a book just barely so old as to be in the public domain:
We find ourselves in the possession of certain advantages, not simply material advantages, but advantages of education, of travel, of society, of culture, of the graces of life, which advantages are not possessed by numbers of our fellow-citizens whom we feel to be as deserving as ourselves. We believe them to be morally as good as we are, and perhaps not infrequently better. We see that they are endowed by Nature with equal or superior intellectual powers. They often work as hard as we do, and if we take into account the disagreeable conditions of their labour, the precariousness of their employment, and the constant proximity of want, their work may fairly be called, if not harder than ours, at least more unpleasant. On any comprehensible theory of justice it certainly seems that, unless we fare better than we deserve, they fare worse than they deserve. Our fathers appear to have accepted this dispensation without questioning it too particularly. They received their blessings as by the grace of the Almighty, and left the justice of his treatment of the poor with him. Possibly there was in this somewhat of the disposition of the Pharisee to be thankful over not being as other men are; but at all events this is not our attitude. So far from being thankful for our own favoured lot, we complain that it is too favoured, and that others who are as good as we are do not share it.
Now, this selection is spread across the second and third pages of an 1897 book called "Industrial Freedom" by one David MacGregor Means. Like you, I'd never heard of either book or author five minutes before I wrote this, nor did any magic go into the selection of the passage. It was, simply put, there. Now let us see what we can do about it. We'll start with synonyms. A thesaurus is helpful here, but you'll do as well to rely on your own vocabulary if you've invested fair labor into building it up for the task. We will select big words throughout the piece, and replace them with other big words (or not so big words, possibly even a string of small words simply defining out the big words) possessing approximately the same connotation; and we will take care that any particular big word appearing many times in the original is equivalently replaced each time in our version:
We find ourselves in the possession of certain advantages, not simply material advantages, but advantages of education, of travel, of society, of culture, of the graces of life, which advantages are not possessed by numbers of our fellow-citizens whom we feel to be as deserving as ourselves. We believe them to be morally as good as we are, and perhaps not infrequently better. We see that they are endowed by Nature with equal or superior intellectual powers. They often work as hard as we do, and if we take into account the disagreeable conditions of their labour, the precariousness of their employment, and the constant proximity of want, their work may fairly be called, if not harder than ours, at least more unpleasant. On any comprehensible theory of justice it certainly seems that, unless we fare better than we deserve, they fare worse than they deserve. Our fathers appear to have accepted this dispensation without questioning it too particularly. They received their blessings as by the grace of the the Almighty, and left the justice of his treatment of the poor with him. Possibly there was in this somewhat of the disposition of the Pharisee to be thankful over not being as other men are; but at all events this is not our attitude. So far from being thankful for our own favoured lot, we complain that it is too favoured, and that others who are as good as we are do not share it.
....becomes....
We discover ourselves in the ownership of various circumstances which give us a head start against our fellows, not simply material circumstances, but circumstances of schooling, of mobility, of human institutions, of historical and traditional influences, of the blessings of life, which circumstances are not had by numbers of our neighbors whom we feel to be as meritorious as ourselves. We believe them to be morally as good as we are, and perhaps sometimes better. We see that they are blessed by Nature with equal or superior acumen. They often work as hard as we do, and if we take into consideration the unenviable environment of their toils, the uncertainty of their job stability, and the unending nearness of scarcity, their work may fairly be called, if not harder than ours, at least more distasteful to partake in. On any understandable theory of fair outcomes it certainly seems that, unless we fare better than we are entitled to, they fare worse than they are entitled to. Our forebears appear to have accepted this way of the world without enquiring into it too deeply. They accepted their blessings as by the grace of God, and left the justice of his treatment of the poor with him. Possibly there was in this somewhat of the disposition of the Pharisee to be thankful over not being as other men are; but at all events this is not our worldview. So far from being thankful for our own favoured lot, we complain that it is too favoured, and that others who are as good as we are do not share it.
Now you may notice that some of the "synonyms" tend to alter the meaning of the sentence -- but it remains an intelligible piece of writing, which is the point of the exercise. You may note, as well, that certain passages went unchanged, and this is for reasons which will become apparent a little later on. But some synonyms having been put in, let us shift our attention to grammar and word order. Taking just the opening sentence:
We discover ourselves in the ownership of various circumstances which give us a head start against our fellows, not simply material circumstances, but circumstances of schooling, of mobility, of human institutions, of historical and traditional influences, of the blessings of life, which circumstances are not had by numbers of our neighbors whom we feel to be as meritorious as ourselves.
We can see that it's quite long, and could stand to be split into two or three sentences, which could then be fluffed out incrementally with meaningless sentence fodder, and expanded further with a few sensible synonym substitutions. And, in the same breadth, we can look at these sentences as clauses, and experiment with switching around the objects and subjects to suit us:
In the examination of our lives, we may discover that various circumstances which would undoubtedly seem to give us a head start against our fellows have fallen, quite by happenstance, into our laps. Ranging from circumstances of personal mobility and superior schooling, to access to beneficial human institutions, historical and traditional influences, indeed of all the blessings of life itself, these are much more than the mere circumstances of wealth and comfort. At the same time, as human observers of our own journey of life, we simply can not help but to note that for vast swaths of our neighbors, whom we may feel to be as meritorious as ourselves, comparable circumstances are not to be had.
Now let's compare this with our original material and see how far we've managed to differentiate things:
We find ourselves in the possession of certain advantages, not simply material advantages, but advantages of education, of travel, of society, of culture, of the graces of life, which advantages are not possessed by numbers of our fellow-citizens whom we feel to be as deserving as ourselves.
Another great way to differentiate your plagiarism is to change the person and tense -- in this case, I chose to move it away from the royal we and the present tense, to the first person singular past:
In the examination of my life undertaken in my youth, I had discovered various circumstances -- which would undoubtedly seem to have given me a head start against my fellows -- had fallen, quite by happenstance, into my lap. Ranging from circumstances of personal mobility and superior schooling, to access to beneficial human institutions, historical and traditional influences, indeed of all the blessings of life itself, these were much more than the mere circumstances of wealth and comfort. At the same time, as a human observer of my own journey of life, I simply could not help but to note that for vast swaths of my neighbors, whom I knew must be as meritorious as I, comparable circumstances were not to be had.
Okay then. Good stuff, let's apply this to (most of) the rest of the selection:
I distinctly recall having thought to myself: "but these people, they are at least as possessed as I of wholesomeness of character, perhaps sometimes of superior character; many are naturally gifted, their acumen matching, even exceeding my own, their diligence rising naturally to the surface and suffusing their work ethic." In attempting to develop an understandable theory accounting for what ought to be fair outcomes, a theory which would account for the disparities of their circumstances as compared to my own, I found myself forced to consider that despite their mental and attitudinal gifts it unquestionably appeared that there were others who were set upon by uncertainty as to their job stability, by an unending nearness to their thoughts of scarcity, and most of all by an unenviable environment in which to practice their toils. If their toils were not more demanding of time and effort than my own, they had to at least be acknowledged as less desirable to partake in. Were I to examine their lot under anything resembling the fairness of outcomes that my heart desired, I had to confess that either I had been placed by chance into a better situation than any to which I could claim to be entitled, or my neighbors were placed in a far worse situation than that to which they were fairly entitled.

But in my studies I became aware, as well, that this dilemma was hardly born with my consideration of it. I learned how the forebears of the society I called my own had wrestled with the same quandaries, and in the end appeared to have simply learned to accept this way of the world without continuing to enquire into it too deeply. They deferred to providence to provide for the needs of the underprivileged, accepting the blessings on their own homes as God's grace. Possibly there was in this somewhat of the disposition of the Pharisee to be thankful over not being as other men are; but at all events this is not our worldview. So far from being thankful for our own favoured lot, we complain that it is too favoured, and that others who are as good as we are do not share it.
Almost at the home stretch, but what about the bits that have yet gone unchanged? First, that line about the disposition of the Pharisee seems too particular to reword to the point of being unrecognizable, so I'm just going to chuck it altogether. As for the last sentence, I don't need to change that at all. Why not? Because I'm going to make the ballsiest signature move available to the plagiarist: I'm just going to throw quotation marks around it and attribute it to its original author. Then another lead-in line of more blatantly pinched introductory fluff, a poignant outtro, and we're done plagiarizing for today.
It was the Greek philosopher Socrates who famously declared, "the unexamined life is not worth living." And so it is that we are indeed compelled not only to examine our own lives, but those of others to develop a frame of reference by which we may evaluate the worth of that which we do.

In the examination of my life undertaken in my youth, I had discovered that various circumstances -- which would undoubtedly seem to have given me a head start against my fellows -- had fallen, quite by happenstance, into my lap. Ranging from circumstances of personal mobility and superior schooling, to access to beneficial human institutions, historical and traditional influences, indeed of all the blessings of life itself, these were much more than the mere circumstances of wealth and comfort. At the same time, as a human observer of my own journey of life, I simply could not help but to note that for vast swaths of my neighbors, whom I knew must be as meritorious as I, comparable circumstances were not to be had. I distinctly recall having thought to myself: "but these people, they are at least as possessed as I of wholesomeness of character, possibly as often as not of superior character; many are naturally gifted, their acumen matching, even exceeding my own, the diligence of their hearts rising naturally to the surface and suffusing their work ethic."

In attempting to develop an understandable theory accounting for what ought to be fair outcomes, a theory which would account for the disparities of their circumstances as compared to my own, I found myself forced to consider that despite their mental and attitudinal gifts it unquestionably appeared that there were others who were set upon by uncertainty as to their job stability, by an unending nearness to their thoughts of scarcity, and most of all by an unenviable environment in which the practice of their toils must be exercised. If those toils to which they were relegated were not more demanding of time and effort than my own were of me, they had to at least be acknowledged as less desirable to partake in. Were I, with a frank resolve, to examine their lot under anything resembling the fairness of outcomes that my heart desired, I had to confess that either I had been placed by chance into a better situation than any to which I could claim to be entitled, or my neighbors were placed in a far worse situation than that to which they were fairly entitled.

But in my broader studies of the human condition, I became aware, as well, that this dilemma was hardly born with my consideration of it. Indeed, I learned how the forebears of the very society I called my own had wrestled, with each passing generation, with the same quandaries, and in the end appeared to have simply learned to accept this way of the world without continuing to enquire into it too deeply. They deferred to providence to provide as it may for the needs of the underprivileged, accepting the blessings on their own homes as something of a divine blessing. I can not help but be reminded of the conclusion drawn from similar circumstances by David MacGregor Means, in his work on "Industrial Freedom," penned over a century ago: "So far from being thankful for our own favoured lot, we complain that it is too favoured, and that others who are as good as we are do not share it."

In summary, though my examination of my life led me to conclude that circumstances beyond my control had placed me in a position of relative privilege, this examination ultimately led to me to feel thankful, and not reproachful, that such was the place into which the fickle hands of fate had deposited me.
Now, notice: with the above, I haven't communicated a god damned thing which was not already in the original. I've just done it with a greater abundance of words, and in a more self-important tone (that being one direction, as I could just as well have gone the opposite way and spoken in a dispassionate third person of what man observes of man).

And that, folks, is how you plagiarize, and indeed, how some of our greatest writers have surely gotten away with it for all their careers.