The official word from Adsense on ad targeting is
“We go beyond simple keyword matching to understand the context and content of web pages. Based on a sophisticated algorithm that includes such factors as keyword analysis, word frequency, font size, and the overall link structure of the web, we know what a page is about, and can precisely match Google ads to each page.”

• Use “keyword-rich” copy as far as possible on all pages
• Contain your keywords or phrases in complete sentences - avoid using them in bullet point lists (like this one!)
• Emphasise your keywords with larger font sizes
• Make your inbound anchor text keyword-rich. This means when pages (your own or other websites) use your keywords as the anchor for the hyperlink. For example a link to this site would read ‘Google Adsense Maximise Revenue