Mike Gutner from Google (Adsense Optimization Team) provide us a proven Adsense success formula. Here you have the 3 simple and easy steps

1. A content-rich page = Highly-targeted ads
2. Highly-targeted ads + Interested users = Healthy clickthrough & conversion rates
3. Healthy clickthrough & conversion rates = Success!

So in summary all you need is

A content-rich page + Interested users = Success!

It is surprising how many people cannot use this super simple equation.