If you advertise on pay-per-click search engines -- like Overture.com -- here's easiest way to minimize your risk and maximize your profits:
Visit Overture.com and click "Advertiser Login" at upper left. Then, near lower left corner of page, click on Search Term Suggestion Tool.
Now here's fun part: pick a keyword phrase that your prospects are searching on. For example, if you sell a business opportunity, you might pick "opportunity".
Type that keyword into Search Term Suggestion Tool and click blue arrow. You instantly get to see all of keywords that Overture visitors searched on last month, how many searches were done on each word!
Why is this so valuable? At first, you might think "secret" is to bid on most popular keyword phrases ... ones that receive most searches.
True, this will bring you lots of traffic, but it will also cost you a fortune! After all, these words are also most competitive. So they command highest bids. At time of this writing, #1 listing under "business opportunity" costs $1.36 per click!