Working directly with an advertiser

[JasonN]

I received an email today from a marketing manager at a prominent retailer in my niche asking about advertising on my site. So far I've only used Google AdSense, so I know very little about working directly with advertisers. I want to make sure I don't end up giving away too much ad space for too little money, so I want to read up on it now. I will search this forum and on Google for advice, but I know how hard it is to get to the best resources right away.

Can anyone offer your own tips on how to handle this kind of advertising, or point me to the best places to read about it?

Thanks!