Google Adsense is one of the most user-friendly types of advertising to add to you website, but many people don't spend a lot of time making it effective. In this article, I'll share tips that I've found helpful and link you to additional resources.

1. First of all, the three main aspects you have in your control are ad size, ad colors, and location placement. All of these aspects will can have an impact on your results, so it helps to do some study of how website viewers react to these aspects.
2. With ad sizes, I definitely recommend exploring outside the default ad size. (In some situations, banner ads can automatically be overlooked by viewers who are used to seeing them often.) One major strength of Adsense is it gives you a lot of text ad options, which draw viewer to them
   by their topic and content.
3. With colors, blending ads into my websites have worked best for me. Blend your border color to the color of the page. Whatever color you have for your content links, match that to the title color for your ads. This creates a pleasant appearance for your blog or website, and that impacts your click-through and people coming back on a regular basis.
4. Most website viewers scan from top-left to top right and then move to the center (where most websites have most of their content). Keep that in mind when you place your ads.

Source: http://www.ehow.com/how_4608428_use-google-adsense-effectively.html