1. Less is more - Some of the most recosgnised brands in the world use a simple marque or logo type - think how simple the Nike tick/Swoosh is.
2. If in doubt - simplify! (see rule No.1) Strip away anything that may make the logo look fussy or overly complicated.
3. Will the logo remain timeless. A good logo for me should remain timeless, it is all to easy to design to a trend but a logo should have longevity.
4. Scalability - Consider how the logo will look small (on a website for example) and large.
5. If it works in black it should work in any colour.