[Source: I founded isocket - we power direct ad sales for the web's best publishers like Microsoft, Aol, etc.]

If your application is new and the traffic still modest, you should focus first and foremost on building your audience before worrying too much about ad monetization. And the typical first step is to throw an ad network on, which will take care of the pricing economics for you behind the scenes.

If you're ready to do direct ad sales, then some good starting rules of thumb for a smaller site are:
* $1-3 CPM.
* Double what you were making eCPM from networks like AdSense.
* Ask a potential advertiser.

We always encourage new publishers to start off with a price low enough that, given your audience, you are super confident you could spend an hour calling potential advertisers and at that low price SOMEONE would take it. Start there, repeat, move upward.