For best click-through results, you want to optimize your Web site. Remember that you can’t host AdSense units on pages that entice or tell the visitors to click the ads. You can, however, position the ad, highlight the ad, set colors and borders, and add graphics such that the user’s attention is drawn to the ad. Google AdSense ads are designed to complement your site’s content, not be the focus of the content.
Excited about AdSense and want to host as many ads as possible? Great idea! You can have multiple ads on a single page, but within limits. You can have a total of three ad units + two search boxes + one link unit + four referrals.