1. The larger the website the better. Any website with thousands of pages will receive many more hits from the search engine than a small site.
2. Free content is a great way to go when building a site... articles, books, software and so on.
3. A few inbound links will ensure higher rankings thus bringing in more money every month.
Now for a few of those top secrets....
4. Place Adsense on 90% of your pages.
5. Vary the type of Adsense Ads on your pages.
6. Place at least one Adsense ad above the fold on your pages
7. Experiment with pictures above each Adsense ad.
8. Experiment with the ads blending into the page and standing out.
9. Some statistics have shown that the large rectangular Adsense ads get the most clicks.
10. If building a website from scratch do research on the most profitable keywords for your websites topic.
Above I have only listed a few of the tips and secrets on Adsense. There are many good books and videos currently online that will help increase your Adsense income significantly of which you should look into if you are serious about making Adsense another of your full time income streams.
The final thing I would also recommend is Adsense tracking software. I use software constantly and it has easily doubled my Adsense income within the last six months alone.
As with any business or income proposal, make sure you do your research as this will ensure not only maximum exposure on the internet but also the best possible profits for your websites and online business.