Perhaps the single most important thing that affects your web sites ranking is incoming links. However, it isn’t as simple as just getting incoming links pointing to your site, the links need to come from credible sources. To boost relevancy, links surrounding text need to contain industry phrases and the link itself can give you a boost if the linked text contains a key phrase that you would like your site to be known for. See: URLs and Linking for SEO
Before I start working on directory listings I use Google’s Webmaster tools (look under >Statistics >What Google Sees to see what phases the site is known by and then under >Statistics >Index Stats to run the link command) to find any existing links to my client’s site. I extend this you Yahoo and search using “link:www.yourwebsite.com” (this command also works on Google). You need to try both the www and non-www version of this (see mod rewrite rules for uniform spidering ) to get all the occurrences and be sure to search on any old URLs you may have and you can competitors links. You should also try searching on current and past phone numbers and street addresses to find any directory listings that do not have links. Frequently I find that un-linked listings can be updated with links and don’t miss an opportunity to add relevant categories (home builder, building contractor, …) .
One of the easiest places to get relevant incoming links is directories and buyers guides. When setting this up for a client I frequently search on terms such as “(industry) buyers guide” or “(industry) directory”, inserting the industry where indicated. Superpages is a big one that you need to pay attention to because its content is syndicated in many locations. Another tactic is to search competitor’s names, URL, and phone number to find where they are listed. Many sites offer free listing and links, others are looking for a fee.
So how do you know if you want to spend the money for a listing or not?? If the directory, buyers guide, etc turns up the first page of Google for a key search term in your industry, you need to consider that the site is valuable both as a way for customers to find you, and as a relevant site to help your Google ranking. From there, it’s a matter of how much does your product sell for and how many additional sales do you feel the listing will generate.
Lastly, note where you find sites that allow customer feedback and send links to customers with a request to add a posting about your company (the more the better). This may not help your ranking directly, but more content may mean more search hits and ultimately more traffic to your site.