Make Sure at Least Some Display Ads Are above the Fold

When you design the layout for your site, consider the ad placement in advance. You don't want your ads to get in the way of your content or take away from the user experience, but at the same time, they need to be placed where they can be visible to provide greater value to marketers. The most visible space on your site will be the area “above the fold”—the portion of the page that appears on the screen when a user first arrives, before he or she scrolls down. Where the fold is depends on the user's monitor size, resolution, and browser window size, so it could be different for each visitor. Figure out where the fold is based on the two more common resolutions (600 pixels high and 720 pixels high) and make sure you have at least one if not two ad placements visible in this space. Advertisers will want these placements most often, and you can typically charge higher rates for them.

(MLA 8th Edition)