Edit: mods, I just saw there is a book category. Feel free to move this post.
I did a search in the forums and couldn't believe it hasn't been listed. But by far the best "self help" book I've ever read is The Slight Edge. In fact, it's one of the best books I've ever read, period. I was re-reading it last night (for about th 7th time) and thought it was ridiculously applicable to MMM, especially those of us with a ways to go.
The basic premise is that it isn't the BIG leaps that lead to success but the small everyday things that you do consistently over time that get you where you want to be. Basically a mindset.
I originally bought it to help get in shape but find it equally, if not more applicable to FIRE. Interestingly enough it starts off with the idea of Compound Interest and investing money. It works for other aspects of life as well. For example, taking the bike to work one day won't be life altering or save all that much in $. But after a year you'll find you've saved loads of money taht would have been spent on gas and maintenance for a car and you are more in shape. Pretty soon you may find you don't need the car.
5-stars on Amazon says it all:
http://www.amazon.com/Slight-Edge-Turning-Disciplines-Happiness-ebook/dp/B00GDKN3T6/ref=sr_1_1?ie=UTF8&qid=1412798117&sr=8-1&keywords=slight+edgeIt does get a bit repetitive with the analogies, but that is what I personally find to be useful. Take what you need.