I think that a VisualStyle can be broken into the follow general bits.
1. Frames and Controls
2. StartMenu and TaskBar
3. XPShell (Logoff/Shutdown Dialog and Task Pane)
4. Toolbar Icons
5. Shell Animations
Depending on the author, I think that most start by working with #1 or #2. #3 isn't necessary, but since most people are using WinXP, skinning this area gives your skin a "complete" feel to it. #4 is usually skinned by the authors who have a greater skill at graphics (I don't so I skip it). #5 involves another whole process of creating avi files (I avoid this as well). If you're looking to upload skins here, I would suggest that when you got a good one that at least #1-3 be skinned and play with it in every imagineable situation you can think of, to try and find the little things that look right in SkinStudio, but can get goofed when in use. If you have questions, concerns, cares or worries, just post a message in the Skinning Discussion MessageBoard. Koasati and Hippy seem to hangout there and they're really good at helping folks fix skinning problems

Good Luck and Have fun