Promoting a web site involves several things, each have equal importance and should be followed up, here are a few places to start:

Search Engines
The number one place most people will find your site is through search engines.  You can submit you url to most of them for free, it does take some searching at times to find the place to add your url, but most of the times it is usually a simple process.  Don't be frustrated if it doesn't get listed immediately, there are thousands of people doing the same thing, and much of the time the web site has to meet specific criteria before it will even be listed, please see the bottom of the page for more information on this.

Links Between Web Sites
Exchanging reciprocal links is also a very good way to get traffic.  You should look for other web sites of the same subject/theme/content as yours.  You will be getting targeted traffic to your site which is of course much better than raw hits.  Banner exchanges "such as this web site" web rings, and old fashioned regular links between sites should be things to look into.

Traditional Media
All of your business cards, brochures, traditional and online ads should have your url in it somewhere, after all a web site can convey much more than what any ad will do, it is your online sales force and presentation team.

Preparing Your Web Site
The number one reason peoples web sites don't get noticed, listed in search engines, or have problems getting others to exchange links with them is content, meta tags, and layout.

The www is a great place to show off your company, but unless your only goal is to have an online brochure, you will need much more than what you would distribute through the standard media.  The idea is to make your web site a portal catering to the interests of the visitors.  If the only thing you have is products, services and prices, the only traffic you will ever get are people that are only interested shopping and nothing more.  Think of ways to either inform them about the field, services, or other relevant information and/or entertain them through other related aspects, just keep a common theme.

Search engines for the most part not only read the content at the site, but the meta tags built into them to decide if and where to place them into their data base.  They limit the volume of awebfiles in any given category, so you may have some competition to content with to get listed at all, much less ot be listed higher up on the search results.  One way around this is to use the back door approach, find something related to what you are doing, but has less competition, even if it is a few extra outside pages, just make sure it links into your main site, I am not saying using scripts that redirect people to the site you want them to go to without their consent, but find a way to bring them in to your general area and make sure they do have a clear link to your main web site.  You now have another reason to offer the additional pages to your site.

Layout
Lets face it, people are for the most part very visual, if the layout of the site is bland, or looks home made, people will not be very impressed, sometimes you only want information with no bells and whistles, that is what the "text only" version of your web site is for, but keep the style and layout pleasing to the eye.  Consistency within the rest of the pages helps avoid confusion also, don't change the buttons and links around all over the place from page to page, keep to a common theme.  There are way too many web sites that take hours to analyse what they are trying to convey, they look like a big listing of free for all banner ads with no clear direction.  In today's www, you have to specialize, and the more of an expert you appear online in your field, the more sales you will make off line, so keep this in mind before promoting your web site.