How to DJ using CDJ equipment
Note: Before reading this, I would highly recommend reading the writeup Loquacious wrote above. He covers the general knowledge of DJing in a far more coherent manner than I could ever hope to be capable of, and it is applicable except for some details to DJing with CDs.
While I've noticed that the art of vinyl DJing is well documented in E2, I notice that the art of DJing using CD's is woefully underrepresented. So allow me to enlighten the community on the particularities of using CDs to DJ.
(Note: This information was compiled and figured out through pure experimentation using a pair of Pioneer CDJ-500 CD players and a metric fuckton of psy-trance CDs. YMMV)
First, we'll be referring to the decks as "CD-A" and "CD-B". All of the basics of vinyl DJing apply, of course, at least in the sense that a track will be playing off CD-A, and that you will be mixing in another track from CD-B.
Now, while CD-A is playing, use the search buttons and the jog dial to find the downbeat on CD-B. You'll want to make sure the crossfader is completely toward CD-A, and that you can only hear CD-B through your headphones. Please note that there are 75 frames per second on a CD, as this slight distinction from vinyl can be important. You'll want the track to be paused when you are close to the downbeat, so that you can search it frame by frame using either the search buttons (a tap will move the track one frame) or the jog dial. The correct frame to cue the track to will either be the frame that you initially hear the downbeat, or the frame immediately before. Once you have it on the correct frame, press the cue button.
OK, remember that really annoying noise you were hearing of the CD player playing one frame over and over again? That should be gone now. If it isn't, you did something wrong.
Now, the play button should be flashing on CD-B. This indicates that the track is cued and ready to go. You have two, possibly three ways of starting the track.
A. Press and hold the cue button. This will play the track for as long as the button is held down, and returns the track immediately to the cue point when released. This is great for when you are beat-matching your tracks, but I wouldn't recommend it for the live mix, unless you have more than two arms.
B. Tap the play button. An important piece of information here is that the track starts when the button button is pressed down, not when it is released. You can return the track to the cue point by pressing the cue button at anytime.
C. Use a fader start. This option is only available using a DJM series mixer with a CDJ series CD player by Pioneer. (Not quite true. Apparently there are a few other mixers and maybe cd players that offer fader start.) This works by turning on the fader start option on your mixer, and then simply moving the crossfader toward CD-B. I personally find this option to be unacceptably inaccurate, in both timing and volume levels. However, since returning the fader completely back to CD-A also returns CD-B back to it's cue point (or vice versa), this option could be used to create some interesting effects.
Now comes the beatmatching part. You'll of course be using either the play or the cue button to start (as you don't want everyone to hear you putting everything together) so go ahead and drop CD-B in your headphones. Instead of pulling or pushing on the record like with vinyl, you'll be using the jog dial to adjust the track. The pitch fader is identical. Note with the jog dial that one rotation always, *ALWAYS* equals one second of time on the CD. You can use this to experiment with 'sliding' the track back and forth, and if you memorize the position of the dial when the track is beatmatched, you can get a pretty good visual representation of the 'drift' between the two tracks by comparing it by how far the jog dial position drifts. Once you have everything beatmatched comes the fun part.
THE MIX!
Again, you have a couple of options. A fader start is a possibility, especially if you feel like teasing the first few measures of CD-B a couple times. If you really feel like getting fancy, you can use the looping function to set up the mix, but that is another subject for another node. Right now we'll concentrate on a straight mix.
If you want to, you can drop the track in your headphones, adjust them, and then fade into the speakers slowly. But with CD decks you have an option that I don't think is feasible on vinyl. (Update: It is feasible.) If it is feasible, CDs certainly make it easier, possessing the ability to drop the beat, at speed, in less than 0.01 seconds.
If you're feeling particularly brave (and skillful) you can try dropping the first beat live.
The first way to do this is, of course, using a fader start, but like I said, this method strikes me as not being very accurate.
The other method is, with CD-B cued (And hence silent. Trust me, check the input levels on your mixer. It is sending *NOTHING* so you can do this.), move the crossfader over until it is where you want it to be when you drop the track. Ready yourself on the play button, and then press it so that it hits bottom at exactly the point where you want the track to drop in.
While this method of mixing sounds *HELLA* cool when done correctly, the problem is that a split-second discrepancy on the drop can mean that you're opening a mix with a trainwreck. Ouch... But like I said, if you're feeling brave it's well worth the risk when you pull it off.
Oh, and one last thing. If some asshat attempts to belittle your skill and dedication to the art due to the fact that you spin CDs, kindly and subtly break their fucking jaw. You've worked just as hard and with as much dedication as any vinyl DJ, and there's no reason why you should take any shite from anyone over your choice of medium. Remember: They had the exact same attitude towards electric guitars when they were first invented. And acoustic guitars are the standard in guitar-based music now, right?
Oh, wait...