How to ensure that your site to display relevant Adsense ads
Based on personal experience and knowledge, if you find that your Adsense ads are not showing relevant stuff related to your site, there could be due to some factors which you need to look into in order to optimize your content, so that Google displays relevant ads.
1. Keyword density : Have a keyword density of around 3-5%,
2. Name the page/directory the same as your main keyword,
3. Use H1 and bold tags as headings for your main keyword,
4. If you have images, name them after your main keyword, and,
5. Have relevant content related to your main keyword.
If you have very specific keywords, there could have problems too as the ad database may not have relevant ads that are related to your keyword, hence Adsense will display ads which you think are irrelevant.