1) Paper is your friend! - Sketch first, build later.
2) If you don't know if something looks good, delete it.
3) Less is More. If you don't believe that then try this one: Less is Faster.
4) Design for the target audience.
5) Build in png. Then compress for uploading. Save both.
6) A 400*200 graphic shrunk to 200*100 never looks as good as the same graphic built at 200*100.
7) Use readable fonts.
8) No one reads moving text.