Site promotion is the most important thing you will do, after building your site of course.
You should start by getting listed in the major search engines. This would involve perfecting your meta tags, visiting the homepages of the main search engines, such as Google, Yahoo, AltaVista, Lycos, Excite, InfoSeek, Hotbot, and webcrawler, and listing your site with each of these search engines manually. Never use automatic site submission software or programs to list in these main engines...they are too important.
Next, you should list your site with all of the other search engines and directories you can find. Just do a search for "search engines" or "directories".
Okay..now, you have spent hours listing your page everywhere you can think of...but you still aren't getting many hits on your page...well, there is much more to it than that.
Use a signature file at the end of all your e-mails. This would consist of between 5 and 8 lines, which should contain your name, your title, your website name, your URL, the name of your company, and anything else you want to add...but keep it under 8 lines. Using your signature file, start posting to newsgroups, e-mail discussion groups, message boards, etc. DO NOT SPAM these places and people....post intelligent questions, intelligent answers, or intelligent information that is relevant to the group...never just post an ad, unless you are sure that it is acceptable with that particular group.
Tell everyone you meet about your site. Have the URL printed on your business cards, on flyers, and anything else you can get it printed on. If the URL is short, and easy to remember, it will help.
Exchange links with other sites. Sites that are similar in content to yours are good places to start...but un relevant sites work also. Keep an open mind.
When filling out profiles for online communities, chat rooms, game rooms, etc., be sure to add your URL in there...people do look at those profiles, and many of them will go to your page, just to see what you are all about.
There are billions of places and methods for promoting your site online. You just have to keep your eyes open for them, and take the opportunity when it arises.