Search engine marketing is the art of spending money on search engines to promote your site. Unlike search engine optimization, it doesn't guarantee high rankings on result pages. It does guarantee that what you pay is what you get.

Try spending several hundred thousand dollars to promote a Web site. If a major portion of that budget goes to search engines, it will reveal some useful insights about what to do and what to avoid.

1) Search engine marketing (SEM) is high on response and low on branding. When the campaign ends, the audience numbers may drop steeply.

2) Because it is response-oriented, SEM better at targeting audiences rather than going for mass audiences. If the intent of the campaign is targeting, expect to pay a higher cost per click. Use it for higher value products such as real estate, automotive or employment categories that need more inventory or that have clients who are already paying premium CPMs.

If the intent of the campaign is the pursuit of mass audiences, obviously go for the lowest possible cost per click in order to get the largest volume of responses. Google’s minimum CPC is five cents while Yahoo and MSN charge a minimum of 10 cents.

3) Keep in mind that demand for keywords on search engines ebbs and flows with the season. I have noticed that it is harder to buy keywords for my Caribbean Web site when the tourism season heats up. Bidding wars erupt over keywords and will drive the cost way up.

4) Constantly evaluate the results, at least weekly if not daily. Lower the cost per click you are willing to pay if one of your keywords is getting too high of a response and another one is getting a low response. Otherwise, it will skew the results.

Search engine marketing is one valuable channel in a total promotional plan for a Web site. It serves a narrow purpose, but that purpose is quite useful in building site traffic.