There is a thread at WebmasterWorld named What is your greatest Adsense advice?. In that thread there are many great tips; including:
- Put the ads in prominent places - Blend the ads into your copy, as if they were part of your copy - Read the program policies and the terms and conditions - Don't bury it at the bottom of the page like it's an apology or footnote - Let the visitors do the clicking - Do well with site content, high traffic and repeat visitors - Experiment with banner styles, placement and various pages within the site - Don't sit and watch your AdSense stats, they will tend to fluctuate from day to day, so think long term - Have good SEO'd pages (that is what helps serve up relevant ads) - Use the earnings to invest onto your site