So you're a teenager, and you're feeling a little miffed about something right now? Your parents might have just bought you The Secret to Teen Power. Or maybe you're an adult, in roughly the same situation and have been recommended The Secret? The best piece advice I can give you is to not read it and focus time on schoolwork, housework, homework, a small business idea, practicing for a play, or actually doing something to get what you want out of life instead of reading about it.
The next best piece is to think very carefully while you read it. The Secret and The Secret to Teen Power present some very dangerous ideas to the impressionable.
I read The Secret from a standpoint of wanting to know how it works, because if I am to believe in something I should have a basic grasp of how it works. If you were a pilot, you wouldn't fly a plane without knowing how a wing works, so why should you risk it with your life? I can summarise what Byrne is getting at quite simply as "Live the Universal Law of Attraction."

1. Ask the universe for what you want.
2. Believe the universe will provide it.
3. Receive it.

So... instead of getting off the couch and cleaning you room, believe it will be clean, and your mother might clean it out of frustration (parents, are you still wishing you bought your teen that book now?). It promotes laziness rather than working.
Now here's the scary part... If you truly believe the Universal Law of Attraction a psychiatrist would be well within their rights to medicate you, and class you as delusional. According to Karl Jaspers' definition of psychopathic delusion there are three criteria you must meet to be deemed delusion, and interestingly enough, The Secret seems to meet all three criteria:

1. Certainty - you must believe 100% in your delusion. In the case of the Universal Law of Attraction, you must hold absolute belief that when you ask the universe for something it will come to you.
2. Incorrigibility - with 100% belief comes 100% determination to stand by your belief even with proof that it is false. In the case of the Universal Law of Attraction, you must stand by the belief that it will come to you, and that the system works.
3. Impossible - your is implausible or impossible. In the case of the Universal Law of Attraction, it is impossible to guarantee that you will receive a large cash payout without having some ramification associated with it.

Hence, any true believer by Jaspers' definition is delusional.
If you still choose to read any self-help, personal development books, or attend a course on the Universal Law of Attraction, I want you to always remember to ask two questions "How", and "Why". Don't be afraid to ask a facilitator or teacher if going to a course. You're paying them to facilitate, and if they can't or won't answer you, they're not doing their job. When you are given an answer, find out why you were given that answer and how it works.
Do not accept anything blindly, do not dismiss anything blindly. A good skeptic, like a good scientist, and a good detective has an open mind and is willing to accept something if their questions can be answered adequately.