On the web, building a web site is not enough. If there are no links to the site anywhere, no-one is going to visit it. The site won't even be listed in any of the search engines without some incoming links. To get traffic, you will need to do some promotion.

Web Directories
The basic part of any promotion campaign, web directories, whist they may not generate much in the way of traffic, will help in your site's search engine ranking.

Pay Per Click Advertising
This is advertising such as PPC Search Engines and contextual advertising. Be warned, it is very easy to go through a substantial amount of money for no reward using these services if you are not careful. Pay per click engines let you pick a maximum budget a day, but, although $5 may not sound like much, $5/day is $150+ per month. Better make sure your keywords are correctly identified, and, in preference, not highly competed on, and that your sales copy is good enough before doing this.

Quality Traffic, not Just Traffic
It's what everyone is after, more traffic to their website. Traffic is easy to obtain, though. Autosurfers, manual hit exchanges and purchased traffic will all send visitors to your website. However, this traffic is just visitors, many of whom will just burn up your bandwidth for no reward. Unless you are receiving decent money for pay per impression advertising, such as banners and popups, this traffic can be totally valueless.

Repeat Traffic
Unless you only require visitors to visit your site once, because you are selling a one-off product, and your sales copy is fantastic enough that they are hooked to buy on the first visit (and if you are regulary doing this, write an ebook explaining how and sell it), you will want visitors to return. If there is nothing of value at your site, visitors may come once, but they won't come back of their own accord. Typically, it is estimated that a prospective customer will be exposed seven times to a product etc. before buying.

Reciprocal Linking
While somewhat frowned upon, and generally thought to not be as valuable as one-way linking (see below) for search engine optimization, a relevant reciprocal linking campaign can be an important traffic generating tool. swap links with sites in a related, but non-competing, business to your own. It isn't really a good idea to link to competitors; although visitors will be interested in your product, there is a good chance you will lose them to your competitor, especially if their website or product is better or looks better than your own. Not a desirable outcome. For example, a web hosting site could link to a site that sells scripts and programs; visitors to one will more than likely use the other, but the sites are not in direct competition. You can also swap links with web directories that require a reciprocal link.

One-Way Linking
Considered the best form of link for SEO purposes, this can also be a good source of traffic. There are a number of ways of getting one-way links. The easiest is submission to free web directories (see above). Another good source is by writing articles relevant to your site or industry. Webmasters and ezine publishers are always in need of fresh content, and will publish your article for free. The hardest way of getting one-way inbound links is by having websites voluntarily link to you.