Google has brought out some great Adsense optimization tips. You can read it here: Google Adsense optimization tips

To increase your site traffic, which obviously will increase your Adsense income, best way to get traffic is to have fresh content at your site. Write your own articles and submit it to article directories like Go Articles etc. To find more article directories, just do a search for "free article directory submissions" on a search engine like Google.

Another way would be to publish articles by other authors that are relevant to your site content. You can find free articles all over web by once again doing a search for e.g. "free site content".

Do this on a regular basis and watch your traffic increase on a steady basis. You also now know all Adsense secrets you will ever need to optimize your Adsense ads so there is no need dig out your wallet for "secrets".