Each lesson builds on the one before it. If you want to master it, your best path is to do the lessons in order, and master each one before moving on to the next.

Start over. I'm sure in this book it says "there is a difference between simply thinking and directing our thoughts constructively, systematically.." or something similar. You can read the whole book but it is not the same as programming it's lessons into subconscious patterns. I haven't completed it or come close but have read it and without a solid foundation you will collapse into your old way of being in a relatively short time. It really sucks that way and I wouldn't wish it upon my worst enemy.