[smiling]

Make a list of the topics that you can create competitive content for. (Example: if the topic is "chemistry" and you pronounce "cation" with a "sh" sound in the middle, then you can't really create competitive content for that topic. :-) If the list is empty, then you're done! (That means it's time to look into multi-level marketing schemes instead of AdSense.)

Pick a topic from the list.

Check the obvious keywords related to the topic in the Overture bid tool and see if more than a couple pay more than $1/click. If not true, go to Step 2.

Now search for those keywords in Google to see how competitive they are. If the page 1 SERPs for those keywords all have >10,000,000 hits and >PR6, and you're starting with a PR0 site, then it's probably going to take you years to rank for those keywords, so go back to Step 2.

Now you've found (probably after quite a long search) that rare thing: a non-competitive topic that pays well. At least, you think that's what you've found. Time to put it to the test and build a website.

Ooops, too bad, the sandbox effect (not saying there is a "sandbox", just saying that as a rule, new websites have trouble ranking well) means its likely you won't be able to rank for squat on this website for quite a while. Put 6 months into it developing content, then go back to Step 2 again and start trying to make your 2nd website while you let this one "age", with only minor ongoing development effort.