If you found irrelevant ads displaying on your pages, that probably is because google's search engine "mis-understand" your page content. You probably need to spend some time on SEO (e.g fixing your page title, adding meta keywords / description... etc). However, Google's algorithm is not 100% bullet-proof and sometimes it may still assign ads that is not exactly what your page is about. The ads may match some parts (or some particular keywords) of your page, but not the main topic of it.

To work around the issue, you can try the section targeting tags introduced by Google. It allows you to suggest which part of your content you want to emphasize or ignore when google do the ad matching. You can use the following tags to wrap arond the content that your want to emphasize:

<!-- google_ad_section_start -->

<!-- google_ad_section_end -->

or use the following to wrap around the part that you want to ignore:

<!-- google_ad_section_start(weight=ignore) -->

<!-- google_ad_section_end -->

How much this can help? You have to try it out on your pages. But don't expect the ads will become relevant shortly after your changes. It usually takes time (days or weeks) for google to crawl your site and update its search index. So be patient.