Here is a very useful list from Darren Rowse of Problogger
10 Ways to make your Blog more Attractive to Advertisers
1. Have an “Advertise with Us” Banner on your site.
2. Keep the ads on your site specific to your site.
3. Show them the banners.
4. Throw up a free bonus ad.
5. Show your site stats.
6. User demographic information. Know your audience.
7. Have an ‘About Us’ section.
8. Don’t use Google AdSense on your site.
9. Keep your blog on topic.
10. Keep your blog professional.
Good luck!