Search-this.com has an interesting article on practices to improve your CSS. Visit the site for all the details, but here are the cliff notes:
- Keep it Simple
- Don’t use hacks unless its a known and documented bug
- Take care of margins and padding on all elements that you use
- Avoid using too much absolute positioning
- Avoid “divitus”
- Avoid “Classitus”
- Validate your code
- Rationalize your code
- Flexibility
- Browser support