piatkow - 9:19 am on Feb 5, 2012 (gmt 0)
1. Visitor intent - are they interested in buying things and in particular the things that are advertised - hence clicking on ads
2. Available inventory.
My music related sites gets clicks when a major concert or festival is advertised and **** all in between. If it wasn't related to a physical business it wouldn't be worth the time to maintain.