Marketing on the Web evolves with lightning speed, but one fact hasn't changed in the past several years: It's still critically important to enable your Web site to be found by prospective customers using search engines.

Two recent studies have found that, in the past year, the percentage of traffic driven to Web sites by search engines has nearly doubled. The average Web site is now receiving between 13 and 15 percent of its traffic from search engines, compared to 7 to 8 percent in 2002. And that's just an average - many sites receive closer to 60 percent or more of their traffic from search engines.

Search engine marketing techniques

Today, there are two main approaches to being found in search engines:

Traditional Search Engine Optimization (SEO) - With traditional SEO, changes are made to your site's content to increase the chances that it gets ranked high in the search engines' editorial (unpaid) search results. A thorough SEO campaign will include an analysis of your site's design, technologies used, navigation and architecture to ensure the search engines will be able to find it and index its content into their gigantic databases.

Another important step in SEO is to determine which search terms (e.g., words and phrases your prospective customers might type into a search engine) are most appropriate to target. You want to select terms that a large number of people are using, but that aren't so competitive you're battling millions of other sites for position. Then, the targeted search terms need to be worked into your site's content in a way that doesn't try to "trick" the search engines.

SEO can be compared to public relations on the Web. The placement you receive is highly credible, since it's an unpaid, editorial sort of endorsement of your site. But results aren't guaranteed - for your efforts, you might reap lots of high rankings, or you might not attain much visibility at all.

Another analogy is that of "buying" site traffic rather than "leasing" it. SEO allows you to "buy" traffic because the work you do to optimize your site this month will probably still be driving traffic to your site a year from now, even if you do nothing else.

Pay-Per-Click (PPC) advertising - With PPC advertising, you literally pay for performance, with "performance" being defined as a click-through to your site. Your site listing doesn't appear in the search engines' editorial results; instead, it appears at the top, bottom or side of the page under a heading that says something like "Sponsored Sites." You bid for your ranking, and when someone clicks on your listing, you pay the bid amount.

A PPC campaign should include bidding on at least the two biggest players in the search engine business, Overture and Google. These two search engines have partnerships with all the other major search engines, so if you advertise on them, you'll be visible in probably 90 percent of search results in this country.

A variety of relevant search terms should be analyzed to determine how frequently they're searched upon, as well as whether or not the bidding is too competitive. The PPC system allows the advertiser to write the title and description of the site that will be displayed - ideally, a different title and description should be written for each search term so that the campaign is highly tailored and targeted.

PPC can be compared to advertising on the Web, since you're buying placement and have a great deal of control over it. However, savvy searchers will know that it is, in effect, advertising and often skip over it to the editorial search results.

Unlike SEO, PPC would be considered "leasing" site traffic rather than "buying" it. PPC can be inexpensive when getting started, but you have to keep paying over time. If your budget gets cut and you stop paying, all your listings (and traffic) will disappear.

Which one should you choose?

So which search engine marketing technique is best for you? If you need to choose one method over the other, here are some guidelines.

Search engine optimization is probably your best bet if:

• You want to spend some time on search engine marketing upfront and have it pay off in the future on conceivably every search engine there is around the world.

• You have a budget to do some work now and want to save money later on.

• Your site is fairly simple, without a lot of complicated bells and whistles.

• You can afford to wait a few months for results.

• You don't want to have to manage or maintain anything on a daily, weekly or monthly basis.

Pay-per-click advertising may be best for you if:

• You want to get up and running quickly.

• You have a promotion where you want to be able to turn a campaign on and off.

• You want to be able to test search terms or offers and quickly see results.

• Your site is search engine-unfriendly and you don't want to invest in changing it.

• You're only concerned with the top 10 or so search engines Americans are using.

• You're confident you'll have the budget to spend for the long haul, and you have time to maintain rankings on a regular basis.

Keep in mind that there's not necessarily a need to choose between SEO and PPC. Here are some strategies for using both of them either independently or together:

• Run a quick PPC campaign first while the lengthier upfront work for SEO is being done. You can test search terms using PPC and see which ones search engines seem to respond to the most, and use this info when undertaking SEO.

• Undertake SEO first, and if you're not happy with your rankings for some search terms, supplement SEO with a limited PPC campaign.

• Use them both together in an effort to be visible in as many places as possible. If you appear twice on the same search engine results page, congratulations! You've achieved a prominent listing in the paid results section (PPC) to gain immediate visibility among people moving through quickly and in the editorial results (SEO) for anyone who may skip over the paid results.

SEO + PPC = strong ROI

Search engine marketing, like most things, is more complex than meets the eye. But it offers many benefits, not the least of which is that it tends to be one of the lowest-cost and highest-impact marketing tools available. In these days of increased importance placed on marketing ROI, that's a welcome thing.

If you'd like to learn more about search engine marketing, a wealth of information is available at www.searchenginewatch.com and www.searchengineguide.com.