It used to be a pain to use adsense on Bloggers because it targets the entire page and will only show ads relevant to the keyword "Blog". Those blog sits usually have very low CPM so it won't amount to any significant amount of money.
Now here is a simple tip for Adsense users. You can emphasize areas of your page to the Adsense Bot so that it will weigh the your highlighted areas more than others. You are not allowed to use this trick to target on irrelevant areas for more profits. This simply gives you more control, although not absolute, to what will be shown on your Adsense ads.
Emphasize to show
<!-- google_ad_section_start -->
Content to be targeted by Adsense Bot
<!-- google_ad_section_end -->
Emphasize to ignore
<!-- google_ad_section_start(weight=ignore) -->