Just kidding---Make a site on one of your hobbies! If it is something you enjoy and search engine friendly, the money will come!
Normally , if you right for anything that you love for about 2 years daily im quite sure you will have a great site which will be making good cash from Adsense ! Olgi
inventory.overture.com/ Find a keyword that is searched for a lot, then create it into a site. This is very MFA though.. if I were I would just create a site out of one of my interests.
Like i sad before do a site in a domain you know about to get experience (on promoting content SEO etc )
Whatever you choose, it has to be about something that you can update your site regularly with new content, and quality content so your visitors keep coming back. Also you're going to want to learn about strategic ad placement if your goal is strictly to earn from adsense clicks.