There's some good tutorials here:
BioRUST.com :: Photoshop Tutorials >> Basic Principles
If you give me a little bit, I can make a huge tutorial on it if you like.

Anyway - a few tips:
1. I am completely self-taught it Photoshop, by reading articles and tutorials, and just plain messing around. It can't hurt anything to make a blank image and mess around with it and experiment with features.
2. When following tutorials, always transpose variables and input values, that way it is more of your image instead of just following the tut.