Pst! Wanna know some AdSense secrets? The only secret is that there are no secrets per se!
Do a search for AdSense secrets and you will be bombarded by a myriad of ads by trying to sell you the answers to making lots of money with Adsense.
Before you buy anything, my advise to you would be to do some research on a search engine and a bit of common sense. There are literally hundreds of forums where you can pick up valuable information, as well as hundreds of articles that have been written on the subject of Adsense.
Most of the answers are out there for you to find it you will put in a little bit of work. If you buy any of the ebooks available out there, you might find one little nugget of information that you may not have seen anywhere else, but I promise you: most of the time everything is out here on the Internet - all you have to do is search for it. Here are some of the search terms that I personally have used with great results:
increase AdSense income
increase your AdSense income
AdSense adsense tricks
What I can tell you from my own experience is this:
1. Ads at the top of the page and on the left of the page perfom better than any other ads. (Take a look at the "heatmap" from the Google link below)
2. Ads without background colour and borders perfom better than ads within borders with background colour.
3. Ads within content pages perform better than any other ads.
4. A search box on every page gives you another chance for earning AdSense income.
5. A blue link at the top of the ad, the ad in black, and the url also in black so that it blends in with the ad copy - also tends to perform well. A black url makes the link stand out and gives you a better chance of someone clicking on it.
Google has brought out some great AdSense optimization tips. You can read it here: Google AdSense optimization tips
Experiment with your settings and see which brings you the best results. Google's reporting has become a lot better in the last month or so, so you should instantly be able to see which ads result in better CTR.
To increase your site traffic, which obviously will increase your AdSense income, the 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 the web by once again doing a search for e.g. "free site content".