Whenever you can, use higher paying keywords.

Obviously, you'll earn more if the average AdWord that Google displays pays more per click.

The question is: how do you get Google to display higher paying keywords?

Well, for one thing, don't get greedy and create pages on unrelated keywords just because they pay more. In other words, don't create a page on 'cell phone plans' on your motorcycle tire site just because 'cell phone plans' pays more than ‘motorcycle tires.’

How to find out which keywords pay best? If you're a Google AdWords advertiser, you can log into your AdWords account and experiment.

If you're not an AdWords advertiser, use a free tool at the pay-per-click search engine, Overture.

Overture’s tool lets you see what advertisers are paying on Overture for each keyword. Sure, Overture and Google don’t pay the same. But they’re not all that different, and this tool can give you a general idea of which keywords will pay more than others.

(Also, don’t’ forget Google’s commission, so you have to allow for their cut on the amount an advertiser pays for each click.)