Google and other search engines attach great importance to link popularity. If a site related to yours, itself well-placed in the search engines, links to your site, especially if the link contains your primary key word phrase, your search engine rankings will improve significantly, especially for that phrase. It's nearly impossible to rank well in Google or stay in the Bing Search Engine at all if you don't have good link popularity.
Google prioritizes their crawl based upon the quantity, quality, and relevance of links pointing to a page. It appears that when you submit a page via Google's submission form, all that does is count as a "link" for purposes of crawl priority. Googlebot (Google's spider) should get to you eventually because there is now a "link" to you, but it would get to you faster if it found more of them (i.e., links to your site). It is also likely that Google will explore your site more deeply (index more of your pages) if your link popularity is strong.
The best way to build link popularity is to make your site such a fascinating, useful repository of information about your products or topic that people link to it unbidden. This refers back to our discussion about content. Theoretically, you could just focus on building great content and give little or no attention to link popularity, yet attract thousands of links. But in most cases, it's necessary to attend to both.
Some webmasters seem to think that the more incoming links you have, the higher your ranking in the search engines will be. In reality, the quality and relevancy of incoming links matter more than the quantity. All other things being equal, a website with a dozen or so quality backlinks may rank higher than one with thousands of low-quality ones.
One way to get backlinks is to set up a themed reciprocal link directory on your site. This means that you link to sites related to yours in exchange for their linking to you. Reciprocal linking should be thoughtful and intentional, with your end users (not the search engines) in mind. If you request a link swap with an unrelated website for the sole purpose of "building up numbers", you are engaging in a misguided task. If I were to create such a directory for you, I would not contact potential link partners in a shotgun fashion, but would focus on quality, related websites.
Although reciprocal linking still works, some SEO authorities suspect that such links may be devalued by the search engines, because they are usually set up merely to boost search engine rankings. Other ways to have web sites link to you without having to reciprocate is to write and distribute articles or press releases.
Want to see who's linking to you or another site? Use this search string in Google: link:www.yoursite.com
Directories used to be quite effective in boosting link popularity, but Google devalued most of them a while back and demoted the PageRank on their internal pages to zero. There are now only a handful of directories that Google respects, and that are worth submitting to. These include:
Yahoo! - It used to be that sites in the Yahoo! directory were displayed prominently in Yahoo's search results. But now Yahoo! shows results from its spider-fed database. In a round-about way, a Yahoo! listing is still valuable, because it tends to boost your rankings through improved link popularity, which should boost your rankings in Google and other search engines. Commercial sites must pay an annual fee of $299 to have their site included. Non-profits can submit for free, but may wait months and still not be accepted. Other worthwhile paid directories include Best of the Web and Business.com.
The Open Directory Project - This is the most important free directory. Google, AOL Search, AltaVista, HotBot, Lycos, Netscape Search, etc. use it for their directory listings. Here are some tips on submitting to the ODP, or DMOZ, as it is sometimes called. With DMOZ, I don’t worry too much about which category is going to get the most traffic. That would be difficult to determine, and the main value of being in DMOZ is the legitimacy it confers upon your site, resulting in a ranking boost in Google and other search engines. So I just try to find the most relevant category. If there are several, then I look at a couple of criteria. Does the category have an editor? (You can check this at the bottom of the page.) If it doesn’t, the submission will come to the attention of the editor in the category next up in the hierarchy. If you have to move several steps up the hierarchy to find an editor, chances are that editor is going to be swamped, and may not attend to your submission for a LONG time if ever. Another consideration is the PageRank of the page and the number of links on the page. You want to favor pages with higher PageRank and fewer links. But again, relevance of the category is the primary consideration. If your site isn’t relevant to the category, the editor isn’t going to appreciate your submitting it there and may reject it.
Your Yahoo and ODP listings make an important contribution to your link popularity, which is critical to achieving high rankings.
Next: Local Search, Google Base, Yahoo! Shopping, etc.