PSDTuts has a very good article on 9 Essential Principles for Good Web Design. It's a good read for all designers, and all people interested in design. I especially liked the example sites in the article!
I strongly recommend reading the article but in summary, the principles are:
- Precedence (Guiding the Eye)
- Spacing
- Navigation
- Design to Build
- Typography
- Usability
- Alignment
- Clarity (Sharpness)
- Consistency
Thanks to Jimish for the link!