The keywords that are used by Google in their Adsense programme have different values, which means that people clicking on some ads will generate more cash for you than on others. So if you can find out which keywords have a greater value, then you can use those that are relevant to your content to help get better returns.
Googlest.com have produced a 13 page document with the Top Paying Google Adsense Keywords which is available to download for only $5.
This is a great aid for those using Adsense, but obviously only keywords that are related to what your blog is about and can be naturally integrated should be used.
You may notice that I have added a new widget on the left sidebar, which is regularly updated with AdSense Tips to help optimise your use of AdSense on your site.