Targeted niche sites that have a clear theme, tend to generate more advertising revenue simply because it is easier to achieve decent search engine placement.
When determining the site's focus, consider how much the advertisers pay for the advertisements. If the site is focused on ringtones, like Ringtone Central , the payout per click is going to be very small. Because ringtones are not high ticket items, advertisers will not spend a lot on pay-per-click advertisements.
With less obvious markets, use Overture to determine how much advertisers pay per keyword. The cost will usually be similar on Google. Search Overture for a keyword then click "View Advertisers' Max Bids" in the top right corner. This will show the Overture inventory and how much is paid per keyword. Because the market has become very competitive, it will be difficult to rank well in search engines with a new Web site that is optimized for the terms that have the highest payout. Consider targeting terms that are moderately priced.
Aged Sites / Time
Over time, as a Web site is spidered by Google, advertisements will generally increase in relevance. In general, older Web sites will rank better in search engines. The closer the advertisements relate to the Web page's content, the higher the "click-through" the publishers will see.
In order to minimize a Web site's maintenance, place the Google generated AdSense code in the Web site template or an "include" file. This will allow you to easily experiment with different advertisement sizes and ad placement, and keep the Web maintenance to a minimum.
In order to know how effective a specific Web site or ad placement is, use distinct channels and subchannels within Google. This will allow you to discern what performs best on a specific Web site. Using channels will tell you what sites are making money, what advertisements are making money and what ad position is the most profitable on a specific Web site. Keep in mind that you should run an advertisement for a full week, in order to properly test its effectiveness, different days of the week will vary the Web traffic so comparing one week to another will give the most accurate reflection of how effective a campaign performs.
When testing different advertisement sizes, placement or color schemes, be sure to leave campaigns in place for one week. Different days will often result in Web traffic fluctuations. Comparing Web traffic week to week will give a clear indication of what ad formats perform the best.
Integrated Ad Placement
Many webmasters have been successful at integrating advertisements into a Web site. The easiest way to integrate an advertisement into a Web site is to remove the advertisement border. This will allow the ads to better blend with the Web page. Google recommends contrasting the link colors with the Web site colors to increase click-throughs. It is also suggested that webmasters randomize the color of the advertisements, so that frequent users will not naturally "filter" the ads.
Number vs Value of Advertisements
Up to three advertisements can be listed on each page.
This decreases the value of the advertisements served, so publishers should cautiously add advertisement units, as it dilutes ad inventory. In other words you want to serve the most expensive ads at all times.
Like Web copy, "above the fold" holds true with AdSense as well. This means that advertisements that appear without having to scroll will be read more frequently. Hot Spots are areas on a Web page that result in a higher percentage of click-throughs. According to Google, the highest paying advertisements are located on the hot spots.
Google does not indicate if image advertisements or text ads perform better, so webmasters are encouraged to experiment with both.
Highest performing Ad Sizes
According to Google the 336 x 280 rectangle, the 300 x250 rectangle and the 160 x 600 sky scraper result in the highest number of click-throughs. Depending on the website's design and layout, publishers may experience different results with different ad sizes, placements and color schemes. Expirement and track the results for each website to maximize the AdSense payout.