Bill Flitter of Pheedo has a great post about the best practices for RSS advertising, based on their 18 months of experience in the field and their hard metrics.
“1. Ads must fit the environment
2. Ads must be relevant and informative
3. Watch the content to ad ratio and unsubscribe rates
4. Tell, donít sell: RSS ads are about creating relationships with readers
5. Be patient: Unlike e-mail, RSS feeds don’t demand to be read.”