Adsense is based on a lot of things.
Google shares about 60% of the adsense revenue with its users which means that for $1.00 click, you'll only earn $0.60. However, this isn't always true because you get even less for Adsense that's displayed in the content network.
The best way to raise your Adsense earnings is to:
A. Get more traffic (which means more chances for clicks)
B. Use high paying keywords
You can log into the Google Keyword Tool to see what advertisers are paying for keywords (CPC). My tip is go after keywords that are at least $1.00 or more that way you're getting a good share of the revenue.