To make adsense focus on certain keywords of paragraph on the page use

The HTML tags to emphasize a page section take the following format:

<!– google_ad_section_start –>

<!– google_ad_section_end –>

And when you want adsense to ignore certain section or words on a page use

<!– google_ad_section_start(weight=ignore) –>

Paragraph here

<!– google_ad_section_end –>

Also note what adsense has to say about this

In addition, please keep in mind that this feature should only be used to emphasize significant sections of your site’s relevant content. It is against our program policies to manipulate the ad targeting to result in ads that are not relevant to the content of your pages.