Actually I think what has helped me the most is three different books:
Lanny Basham's With Winning In Mind
Bernie Pellerite's Idiot Proof Archery
Larry Wise's Core Archery

I don't agree with everything in Bernie's book, but overall is a very good source of information. I think my shooting style is mish-mosh of these three books. I think they all helped my in some sorts.