1) Don't click on your own ads. 2) Don't buy auto or manual traffic exchanges hits. 3) Don't spam. 4) Don't use copyrighted material.
You may ask google for site review by sending email to Google adsense Team at Ask them to review your site and clarify if your site's content or your adsense ads placement are againts google policies or not.
Here's the best, most concise answer of all: READ, UNDERSTAND AND COMPLY WITH THE RULES! Do not think you can outsmart Google - if you break the rules they always find out eventually. Do that and you have nothing to fear.
if your not sure about something then email google before doing it, e.g. a new site to put ads on etc..