Hello,
The hardest thing that I had using adsense was people really weren't 'buying' from another site that I worked on. However, if you don't care about if they are buying and just want people to click on your site, there are other options out there.
For example, if you are trying to sell your coffee of the month club and the landing page (the page that the user enters your site) is about how to roast beans, then they are going to leave. It must be very very detailed. Adsense is purely computer lanuage, it won't assume anything. If the ad campaign is coffee of the month, then make sure the ad and the link all match up or people will leave. You also have to have a quality site or the keywords will cost a ton. You should not be paying more then 15 cents a click. I was using a keyword, but that keyword was NOWHERE in my page, so adsense wanted it to be $5.00 a click. If you improve the quality of that keyword, it needs to be in the content of your page, title, etc. and then the price per click will gone down.
I have stopped using adwords / overture, it was eating my budget alive (this was for a non coffee website that I was doing it for).
Best of luck,