There are various factors which could help you improve your earnings on Google Adsense program. Google has also made couple of posts to help publisher to optimize their Ads for better performance and below is the summary of what Google has suggested.
1. Choosing Ad units
Below are some of the Ad units that are recommended by Google itself and help publisher more revenue. They recommend bigger Ad units as they are more visible and draw more attention of the users.
a. 728×90 leaderborad
b. 300×250 medium rectangle
c. 160×600 skyscraper
All of these units are bigger in size than all other and help improve publisher earnings in a great deal usually. Below is a Video which provides some detailed information as why bigger ads perform well
2.Tie in the Ad units colors to match with your site theme
I normally pay great attention to tie in the Ad backgrounds and borders with the theme of blogs which you can see here and here both of these sites use dark colors and you can see the Ad units placed on the site don’t annoy the readers as they look the part of the Site or more professional. You can watch below Video which would provide you detailed information and tips for customizing the colors of your Ads units.