After you have gotten a few simple customs under your belt, here are some posts to improve your skills, and take your customs to the next level:
8 Ways to Become a Better Customizer
Don’t Toss Those Packages or Twisty Ties!
Helping Hands
How To Make Celebrity Face Decals
How To Make Metal Decals Shine
Levels of Detail
Relocating a Minimate Joint
The One Brush Method
Using a Sharpie to Straighten Your Lines