Adsense !!! ... from 2008till somewhere 2010/2011 i ws in to this and my first pay out is about around Rm600++ where I used to topup to buy my iPhone 3g 16gb which costR RM2.5k ( at the time)... during those time average per month can get around 1k to 3/4k where certain niche can goes up to USD80 per click (yup !! ...ranking is first page of google search) ..But towards the end 2010/2011 google went berserk and band all oaf my accounts and my brother that time..we loose around 15/18k due to unrelease payment. my advise ...study the the trends and look for niche market/keywords that is mostly relevant to us market .. thats where the money is in.Dont cheat especially on traffics.
Produce genuine content and not copy paste from those article repo ..
As some of has said stay under the radar .. don't asked your friends to test click on the ads on your site for testeings ,if possible don't use same iip twice ( use multiple location starbuck/or othe places .use vpn or tor (privacy) ... after got banned its very hard to get the account back ..so becarefull ..google will study you,your site and your visitor behaviour ...since them I've stopped doing adsense so i don't know any tips or update after that period ..just sharing my exp