Ad-Placement :
The ads on your site should be placed as such that it does not distract or annoy user.
Users generally don't like site with lot of ads. They leave the site if they get annoyed.
Make sure that ads on your site appears to be content of your site. This can be done
by using appropriate colored ad. Check out my ad placement for example.

Keywords :
Load your site with enough keywords to get targetted ads. If you don't have enough
keywords then you will get PSAs (Public Service Ads). PSAs, generally bring no money.
Very few person click on a PSA.

Content :
The most important thing about a site is its content. If the content is good, you will
get people who bookmark your page, if the content is not good, user will leave your
site within seconds. Make your site's content simple and to the point. Use content
which attracts most of users like ' making money '.