Pop psychology sells. Infinite market.
If you want your pop psychology book to sell, there are a couple of guidelines to follow :

Choice of title
If possible, the title should capture enough of the essence of your book, without giving the whole content away. (Which, sometimes can be a problem, as there is not always that much content.)

Examples:
A book about differences in men and women : Men are from Mars, Women are from Venus.
Hamster insertion fetish : Beyond Duct Tape
Profoundly_slack commented that an absurd title helps - i.e. Who moved my Cheese
drownzsurf contributed the following beauties :
Transactional Analysis, I'm OK, Your OK and How to be your own Psychologist.
Thanks !

Personality profiles
It is always good to include a personality profile test. A nice selection of about one hundred questions is easily produced and will do the book a lot of good. People love test taking. Compared to the tests in magazines, yours should be much more detailed and tedious to evaluate.
Another feature is the result you want to archieve. Remember your title ? If you write about insecurity ("Should I or shouldn't I ?"), it will hurt sales if people taking your test will find out that they are not at all insecure. Make sure that everybody taking the test lands in either the "Insecure", "Very insecure" or "I am afraid to even learn the result" category. Remember - the design of this test might take some work, but that will be the most difficult thing in the whole book to write.

It's okay !
Make sure to explain to your readers that it is okay to be whatever this book is about. "Everybody is insecure" or "It is okay that you do this thing with hamsters" are the kind of statement you want to give to your audience. They bought your book, so they deserve some positive feedback. Do you want them thinking they wasted money on your book ?
But - even if it is okay, your book will promise ways to change the reader.

Case studies
Have loads of case studies, showing that you have experience in the field.
Let me give you an example, taken from "I bore you, you bore me, we are a boring family"
"After one of my public speeches in Atlanta, a young man came forward with his wife. John and Mary had been married for six years both working twelve hours each in the coal mine. "It's always been the same. Get up in the morning, shower, have breakfast, off to the coal mine, work, shower, go home, eat, go to bed", John said. "But we learned from you that it's okay and we feel much better now.""

Avoid calling those people patients - they are not ill!

Exercises
Give your reasers something to do. Promise them that if they do exactly what you say, their problem (which you said earlier isn't a problem) will go away.
Good excercises involve people not doing what they normally do. They might even include some adventurous or dangerous things. Make sure that in that case, you mention that, even if this excercise is highly succesful, it should normally only done under proper professional supervision.
Once you have done that, do what you like. A book for shy young ladies could include an excercise like this one :
"In our advanced class for shy young ladies, we tell them to apply heavy make-up, wear an highly erotic outfit, drink two or three drinks and visit the local singles bar, then doing what appears to be natural. If you leave alone, you are still too shy. This usually shows very results after the first day and is the most effective method to overcome shyness. Still - this method should only be employed under strict professional supervision."

Mumbo Jumbo
Borrow, steal, invent vocabulary. Categorize people, labelling them something unique to your method. Make the names easy to remember. The art in pop psychology is stating the obvious with different words.
People with a high potential for aggression could be "red", peaceful people could be "blue".
Piece of cake...

Time to upsell !
They bought the book, now it's time for the real money. Mention that people can book courses at your institute, that you travel the country to hold courses everywhere, that other books you wrote will help, too.
If you are very successfull, you can even run a franchise deal !

More info by Profoundly_slack: get a dodgy PhD ! Thanks, Profoundly_slack !

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