A few tips:
1. Wait a little; it takes a while for the AdSense bot to figure out what your page is about. Then it will start serving relevant ads.
2. Make sure that the page concentrates on one topic. If you are discussing several things on one page (e.g., if you have several blog posts on one page), then the bot gets confused and doesn't know what to serve ads about.
3. Try using section targeting so that the bot only looks at the relevant (content) part of your page when deciding which ads to serve.