A couple of weeks ago, OpenX released a study of direct ad selling practices, based on survey data from the OpenX community. If you have not read it yet, it is well worth downloading the study.
In particular, the report outlines five different techniques that publishers with direct ad sales income of more than $5 CPM generally use, and which may be worth considering using yourself if you are planning on selling your inventory directly. For smaller publishers, this is very useful and valuable information to have. Kudos to OpenX for releasing the information!