From my personal experience this is what I have learned from the Adsense:-
1) Forget about placing Adsense Ads if you have a traffic < 1000
2) Only 336 works within the content. Place it in a DIV with flowing text around.
3) The vertical sidebar ads never gets clicked
4) Randomize the Ad position every now and then, this increases the CTR
5) Links SHOULD be blue. Forget about blending
6) Ads should have no borders. It should blend with the background
7) Never read and get disappointed with others adsense earnings. They are not true
8) Never buy Adsense secret tips books. They don't know any better than you.
9) Never keep adsense filters. They will affect the smartpricing of adsense. you earn less if you keep them.
10) Always TARGET ads using section-targetting of adsense.