Bloggers frequently start planning for direct sales too early. The reality is it's not enough to sit back and wait for them to contact you, just because you've got decent (or even great) traffic. Until you can hire a sales team, ad networks can fill in the gap very nicely.
Questions Answered:
How do you set up an adserver to run multiple ad networks in the same ad space?
How do you optimize the various rates from each ad network?
Which are the best ad networks?
How are ad networks different?
Can you really make money with ad networks?
Which ad networks should I stay away from?
How do I calculate RPM for my ad spaces?
When am I ready for direct sales?
What should I look out for when signing up with an ad network?