Having read a number of posts relating to Adsense I would just like to give a few tips that you should follow when trying to create websites that generate an Adsense revenue:
This is the most important part of your process. This is not a hard and fast rule but there are some good ways of estimating how easy it will be to rank for your target keywords. Try to target keywords that have lesss than 50,000 competing pages (in quotes) in Google.
Also, check out the top 5 results in Google for your target phrase. Make sure they have a low Pagerank - Prefereably not more than PR3 and hopefully at least 1 or 2 results will have a PR1 or less.
It's also a good idea to see how many incoming links each of these sites have. This will be a good indicator of how much work you need to do in order to outrank them. Google do not report backlinks well so when analysing your competitions back-links go by Yahoo counts.
Now you know you have a chance of ranking for your keyword(s) you need to find out whether it's worth your time and effort. (This is where many marketers fall down).
Just because you can rank doesn't mean you should. You need to decide if that keyword is a "BUYING KEYWORD". What I mean by this is : If your searching the web for "how to install windows" then the chances are your looking for an article - not to buy something.
But if your searching for "upgrade to windows vista" then it's fairly obvious you're considering a purchase. This means that your site visitor would be far more likely to click an advertisement, thus giving you a much higher CTR% (ClickThrough Rate).
If your keyword(s) qualify for all of the above then the only thing left is to ensure the CPC (Cost Per Click) is satisfactory. There's no point targeting keywords that are only going to generate you $0.05 per click. You should be able to easily find keywords that will earn you at least $0.30-$0.50 per click and often well over $1.00.
If you found these little tips useful then i'll posts some more, and perhaps explain some SEO basics also.