I earned a total of $21.99 from Google's Adsense for the month of May 09. Not too bad for a beginner like me! After one year of trial and error, I have more or less managed to get a constant adsense earnings of a few dollars every month.
I am not too sure whether there are any tricks or tips that I can share. I think updating your site frequently with new information does help. Why it helps I do not really know. Perhaps Google makes your site more search engine friendly thus resulting in higher number of hits and more clicks at the end of the day.