1) You Haven't Asked Anyone
If you haven’t made a concerted effort to contact and exchange links with relevant sites in your field, then you are vastly limiting your site’s potential. Asking other sites and bloggers to link to you is not nearly as frightening as it sounds. Start by putting a link up on one of your pages linking to the site or blog that you are attempting to exchange links with. Then, get in contact with the site owner, usually through email. Let them know that you have linked to their site (make sure to point out the pages where the link appears) and that you are interested in exchanging links with them. Provide the HTML that you would like them to post on their page, so that you retain control of the link text (a very important thing for Search Engine Optimization).
The most important thing however is to provide a legitimate (non-SEO) reason why the site owner should link to your site. Perhaps your site offers complementary services, and by linking to your site the site owner is able to increase the overall utility of his own site. With the double-benefit of increasing the search engine rankings of both sites as well as increasing functionality, you’ll be surprised at how many links you can get!
2) You Try to Do It All
Jeff Jarvis, prominent blogger and author of “What Would Google Do?” once said “Do what you do best and link to the rest.” Pick one or two things that your site does really well. This may mean narrowing your focus a bit (or a great deal). However, if you want people to actually link to your site or blog, it’s very important. No site owner wants to link to a potential competitor. By trying to offer every possible service you can imagine, you are setting yourself up as a competitor to everyone. Instead, choose your top “value-added” items and link to the rest. This will inspire other sites and blogs to view you not as a competitor, but as a complementary site, a site that actually adds value to your own site. Do this and the links will flow in. Of course, you’ll still have to follow Step 1.
3) Your Site is a Nuisance
I have already extolled the virtues of designing your site for ease of use and not distracting your visitors with annoying pop-up or deceptively-placed ads in 4 Things Visitors Look For In a Quality Site and Rethinking Advertsing (Hint: It’s Not About the Money), but let me do so again: if your site delivers annoying pop-ups for your users or has been designed to squeeze every last dollar of advertising revenue from your unsuspecting visitors, other site owners will see through your ruse. No one will link to you because it looks poorly on them when they refer their visitors to such an annoying site. So here again is another reason why designing your site for quality will always bring you a greater quantity of money than trying outright to optimize your ad revenue.
Your Site or Blog Won't Link to Anyone
If you won’t link to anyone, then no one will link to you. Reciprocal linking is motivated by mutual self-interest. Provide a boost to another site’s search engine rank, and send them some of your visitors, and they will be more than glad to link to you. Send them an email asking them to link to your site or blog without first putting a link to their site or blog or your webpage and you are very likely to get an icy cold shoulder.