If you have a quality web site, chances are you're already being linked to and don't even realize it. That's a great starting point however, you must build on that by finding targeted web sites that may be interested in exchanging links with you. A targeted web site will have similar content to yours, but will not be in competition. Create a page on your web site that includes your banners and text link descriptions. If you provide a valuable service, you can be sure your visitors will tell their visitors, their visitors will tell their visitors and so on.
Word of mouth is one of the best forms of free advertising.
Write an article and allow it to be freely published. With each article you write you are entitled to include your author bylines. These bylines are nothing more than an advertisement for you, your products or services and your web site. Many web site owners will publish articles on their web site and include live links to the author's web site. It is well worth your time and effort to spend some time developing as many links to your web site as possible.