Richard Williams' The Animator's Survival Kit [1] is the standard recommendation, I believe - I've also seen animation courses recommend Preston Blair's Cartoon Animation [2]

[1] https://www.amazon.com/Animators-Survival-Kit-Principles-Cla...

[2] https://www.amazon.com/exec/obidos/ASIN/1560100842/

Sorry, a friend got me the book and videos so had no idea how expensive they were... Guess I have just found out I have a good friend :)

here are some excerpts from the videos:

https://www.youtube.com/watch?v=nbtbbdA4kUM&list=PL1A1FEDA47...

also the book is also amazing

http://www.amazon.com/The-Animators-Survival-Kit-Principles/...

and only $30

if you need any excerpts or advice on this stuff, tweet me @jonathanmatthey happy to help :D