Re: "Golf is Not a Game of Perfect" (and his other mental game books) by Bob Rotella
Putting out of your mind is a must read. Very easy read, I read it in 2 days. The next day my putting and my life improved dramatically. Putting is now my strength, where before it was my weakness. Simple stuff really. Just think about what really matters and don't worry about what you can't control. I even gave the book to my teaching pro and he came back to me 2 weeks later all wide-eyed saying he has never putted better in his life. I thought it was ironic that a 13hcp helped a teaching pro get his groove back. And I didn't charge him $80 an hour either.
However, if you want to keep beating your buddies, don't tell them about the book.
Also, I burned a copy of all the little bullets at the end of each chapter and keep them in my bag. When things go a little bad during the round, I whip it out and read over them. Helps a bunch.