More information on Section Targeting can be found here: www.seo-portal.com/section-targeting-for-adsense/2006/07/06/
6. Competitive Ad Filter
Make sure you use the Competitive Ad Filter in your AdSense account to block non relevant or low paying advertisers.
When you just start your blog, you have a high chance of getting weblog advertisers in your AdSense ads. These are of course relevant because they are displayed on a blog, but they are also low paying so you want to filter them out.
To do so you have to login to your AdSense account, go to the AdSense Setup tab and there you'll find a link to the Competitive Ad Filter. Type in the urls of the advertisers you don't want to be displayed on your site and you're done.
7. AdSense Deluxe Plugin
AdSense-Deluxe is an easy-to-use plugin for WordPress 1.5+ (including WP 2.0) for quickly inserting Google or Yahoo! ads into your blog posts, and managing when and where those ads are displayed. You can get the plugin here: http://www.acmetech.com/blog/2005/07/26/adsense-deluxe-wordpress-plugin/