Graywolf's Wolf-Howl: Google Adsense Tips, Tricks, and Secrets: "You can build your website around general topics or niche ones. Generally speaking niche websites work better with adsense. First off the ad targeting is much better. Secondly as you have a narrow focus your writing naturally becomes more expert in nature. Hopefully this makes you more authority in your field.
If this is your first try at building an adsense website, make it about something you enjoy. It will make the process much easier and less painful to accomplish. You should however make sure that your topic has enough of an ad inventory and the payout is at a level you are comfortable with. You may love medieval folk dancing, but the pool of advertisers for that subject is very small (in fact it's currently zero).
Once you've gotten the hang of how Adsense works on a website, you are going to want to dabble in some high paying keywords, you may even be tempted to buy a high paying keyword list. This does come with some dangers. First off the level of fraud is much higher on the big money terms. Secondly there is a distortion of the supply and demand relationship for these terms. Everyone wants ads on their website that make $35 or more a click, however the number of advertisers who are willing to pay that much is pretty limited. Additionally the competition for that traffic is going to be stiff. So, don't try to run with the big dogs if you can't keep up. If you have to ask if you're a big dog, then chances are, you're not. I have used a high dollar keywords report from cashkeywords.com and was pleased with my results (see cash keywords free offer recap)."
