I'm developing a web application which contains banner ads, and I don't know how to teach my clients how much to charge their customers for banner ads. Can someone help with a book or business strategy?
I think this is a good article on the subject http://www.problogger.net/archives/2008/03/27/how-much-should-i-charge-for-my-advertising-space/.
The best thing to do is research what others in your industry are charging for ads of any kind on their websites and see what Google Banner ad rates go for on subject matter comparable to your site.
Once you have all of that you can create a guide for your clients to follow based off of what you have learned.
I ran a large non-profit site for several years and we got into the advertising game. The problem is that there's no one-size fits all answer to this question. Some factors that can influence your efforts:
To answer the original question, unless you formulate a sort of bidding system, you're likely going to have to rely on trial and error. You'll get laughed at several times as you attempt to charge too much, or you'll overfill your inventory by charging too little, then be chastised for raising your rates. It's the reason that I recommend to everyone that unless they're serious about supporting an advertising system to come back to reality (financially speaking) and get onboard with a system like AdWords or DoubleClick. As developers and tech guys, there's so many other ways for us to make really good money!