These tutorials are the way that I do it. There is no right and wrong way, and I hope that you can find your own way of creating - the way that makes most sense to you. In the end - your way is the best way. 

I use PSP7 but any other paint program which has layers will do - you'll need to work out what is equivalent. 

THE SIMS2 TUTORIALS

Basic Techniques

• Creating a Vanilla Game Space
• Removing the Red X from Objects

Wallpapers

• Making Wallpapers in Sims2

Recolouring

• Recolouring a New Mesh Object (Tapestry)

Organizing

• Categorizing Eyebrows and Facial Hair
• Creating Default Eyes*NEW*

THE SIMS1 TUTORIALS

Basic Techniques

• A Introduction to A-buffers
• Fixing A-Buffers on existing objects
• Creating A-Buffers from scratch
• Creating A-Buffers for multi-tile objects

Wallpapers

• Making a plain wallpaper in Sims1