Adsense optimization involves placing Adsense in the best possible position on your site and using the most effective color scheme so as to generate the most number of clicks from your visitors.
Adsense optimization however goes far beyond simply slapping some ad blocks on your page.
It is also very much about your website content. If your content provides absolutely everything that visitor needs, is he or she likely to click an ad? In most cases the answer would be no.
This by no means tells you that the best way to write content is to leave gaping holes in it. Your visitors will not like this and may not return. However it can be worthwhile to not give your visitors EVERYTHING about a particular topic. If you leave them wanting more then they are likely to click Adsense ads to find further information. There is nothing unethical about this and in all reality, it is impossible for one person to cover all aspects of a topic in a single article anyway.
Adsense optimization needs to be tested through the use of channels. Channels can be set in your Adsense account and allow you to track every single ad unit separately. This is vital if you have multiple ad units on a site, which most people do.
By optimizing your Adsense placement, format and colors, you will no doubt increase the CTR and hence your Adsense earnings.