This is a great article on how to improve your CTR (Click through rate) and avoid some common pitfalls on ad implementation, especially for those of us trying to integrate multiple ad network solutions. Its written by someone at Mobclix but the advice is fairly generic. Most interesting to me was learning how ad networks will tailor what they deliver to you and what they pay you based on your CTR performance.
http://blog.mobclix.com/2011/02/24/how-to-increase-your-click-through-rate/