Reddit reviews The After Effects Illusionist: All the Effects in One Complete Guide

If you haven't already worked through Andrew Kramer's Basic Training series, that's a great place to start learning After Effects. Lynda.com is also a good resource. After you've learned your way around the software, the best way to proceed and get a deeper knowledge is to just start trying things. Mess around with different settings and keyframing techniques. If you can think of what you want to do but can't figure out how to do it, just see what comes up on a Google search. The Creative Cow forums are a good place to go if you can't find an answer to a specific question.

As far as books, the most recent that I've learned a lot from is The After Effects Illusionist, which just goes through and does a break-down of every native effect. Very helpful in decoding some of the effects that don't seem to do anything useful at first glance. This book won't be as clear until you have a solid understanding of AE to being with though, so that depends on where you're currently at.