The placement of your ad on a search engine results page is determined by its "Ad Rank" (SERP). There are two factors: your bid (i.e., the amount you are willing to spend) and your quality score. You cannot simply state that you want your ad to always appear at the top of the page since Google will recalculate your ad rank each time someone searches using the phrases that trigger your ad. Rather, it is a shifting objective, and you must examine whatever ad position appears to create the highest ROI for you. Typically, the most desirable ad locations are the top 10 results and the top positioning that permits your ad to appear most prominently on the page. The first three advertisements usually get the best real estate on a search engine's results page.