Links are important to Google, Yahoo and MSN in determining where your site is placed within the search results. As you probably know, the more links, the better you will place.

The engines place a weighting factor on each link. That is, a link from an important site like CNN.com would count for a lot more than Jimmy Bob's personal homepage.

Google calls its importance-scoring system "PageRank," and it's been a fundamental building block of Google's ranking algorithm since day one. Tactically improving the PageRank—or, more generically, your "link gain" across all the major engines—of your homepage and of key internal pages of your site is critical to being well-ranked and thus getting traffic.

Links are the currency of the Web, so it is important to have a plan in place to improve the number and quality of the links to your site from the outside. That is the idea behind link building.

Link building can be approached a number of ways. You can, for example:

• Garner links from vendors, clients, business partners
  
  
• Garner links from other related sites
  
  
• Garner links through general directory entries, like Yahoo
  
  
• Garner links through specific directory entries, like a marketing services directory if you are a marketing consultancy
  
  
• Sponsor organizations and get acknowledgement through a link from their Web sites
  
  
• Create content and syndicate through RSS so that other sites will post the content contained within your RSS feed on their sites with a link back to your site.

It is not just about the importance of the page, or the PageRank score. You probably get bonus points for a link from a topically relevant or authoritative site, so target topically relevant sites in particular when link building.

By the way, the worst kind of link building is sending unsolicited email to Web masters asking for a reciprocal link. Web masters get inundated with such spam daily.

Each page within a Web site is assigned its own PageRank score by Google. PageRank scores run from 0 to 10 on a logarithmic scale, meaning that the gaps between the integers increase logarithmically the closer you get to 10. So, for example, the gap between the 3 and a 4 is quite small, whereas the gap between 7 and 8 is huge in comparison. As such, boosting your PageRank from a 3 to 4 would be quite easy, and going from a 7 to 8 would be quite hard. Another logarithmic scale you might be familiar with is the Richter scale. As you probably know, a 5.0 on the Richter scale isn't such a huge deal, whereas a 7.0 is a very big deal indeed.

You can check your PageRank score several ways. One is using the Google Toolbar, available for download from toolbar.google.com. It works with Internet Explorer (for Windows) and with Firefox, users of which also have access to an alternative toolbar with a PageRank meter available at www.prgooglebar.org.

You can also check your homepage's PageRank score using the Google Directory at directory.google.com—assuming, of course, that you are listed in the Google Directory! If you aren't listed, you can submit through the "Add Site" link at the bottom of the appropriate category page where you wish to be listed.

Listings on Google Directory category pages are ranked in order of PageRank score. This means it is possible for you to see your site make small PageRank shifts relative to other sites in your category, particularly if there are a number of sites listed on your category page. (If you are curious where your site sat in comparison to others listed on that category page in the past, you can get historical PageRank scores using the Wayback Machine available from Alexa at www.archive.org.)

A word of caution: don't be overly focused on what that little green PageRank meter says. PageRank values shown in the Google Toolbar are imprecise, months old and not the same as the PageRank that is used in Google's ranking algorithm. Google realizes that it's really only search engine optimizers who care about the PageRank scores, and they don't want to be too helpful to SEOs. So PageRank scores should be treated as merely indicative, and so you have to take them with a grain of salt.

PageRank as an algorithm is alive and well, and will adapt with the times. One way we can probably expect to see it evolve is with the incorporation of "TrustRank," a concept where a small number of reputable seed pages are used to help differentiate good pages from spam.

There is a tactic called "Google bombing" whereby linking to a site with particular words in the link text can get a site highly ranked for those keywords in the search engines, including Google, Yahoo and MSN. One of the most famous Google bombs has been George W. Bush's biography page on whitehouse.gov being ranked number one for the phrase "miserable failure"—even though neither the word "miserable" nor the word "failure" appear anywhere on Dubbya's page. It was the sheer power of the inbound links with the link text that did it.

Not all links from a high PageRank-endowed page are equally as good. For instance, if there are a great deal many other links on that page that link to you, you will end up with only a small share of the link gain that has been passed down, as you are sharing it with the multitude of other sites linked on that page. The fewer the number of links, the better.