We started running one site with Google Adsense. It didn't generate much money, but showed us what kind of keywords DID generate clicks. We used this knowledge

We started running one site with Google Adsense. It didn't generate much money, but showed us what kind of keywords DID generate clicks. We used this knowledge to start selling banner adverts and that has brought in a lot more. We're not talking fortunes - it brings in around $4000/month, but that passive income helps