Search engine optimization is one of the key elements of a profitable web site.  Most traffic to good websites are through search engines.  To perform well in search engines is therefore by far the best way of advertising your site.  Here are a few important points to keep in mind when you design a website:

Quality content.  There is no way around this.  A substantial amount of relevant content will hit well in search engines over time.  Update your articles regularly (some news feeds may also help).

Find niche markets.  If you start up a new site, keep in mind that the market for the popular topics are heavily saturated.  It might be wise to write on topics where there is not so much competition, where there is room for specialized information.

If you want to earn revenue via sponsored links (e.g. adsense), use the correct keywords.  You can buy keywords from Adsense Heaven.

List your site in SEO-friendly directories (eg. see this list).  Spend time with other webmasters and get quality links to your site from sites with a good page rank.

Use meta tags wisely.  Never repeat keywords in your titles or within your articles.

Use user friendly URL's if possible, e.g. http://www.mysite.com/topic3.

Advertise with search engines (e.g. adwords).

Have a website analyzing program for your site (e.g. Google Analytics) and see what brings people to your site. See what works and what does not.

Use search engine Webmaster Tools (e.g. google Webmaster Tools) and upload a sitemap if possible.

For more webmaster tips, see Google's guidelines.