There are several ways you can earn money from advertising:
1. Join an advertising network. Advertising networks are organizations that aggregate Web sites that offer advertising space, and sell banner ads (and other advertising options) across them. Traffic requirement is often a minimum of 5,000 monthly impressions, although many do not accept sites hosted by free page services.
Burst Media http://www.burstmedia.com
Fastclick (ValueClick). http://www.valueclickmedia.com
Tribal Fusion http://www.tribalfusion.com
2. Participate in contextual advertising networks. Contextual advertising are text ads delivered based on the content of the web page using an automated system.
Google Adsense https://www.google.com/adsense/
Yahoo! Publishing Network (currently in beta and available to US publishers only) http://publisher.yahoo.com/
Quigo Adsonar http://www.quigo.com/adsonarexchange.htm
Commission Junction Evolution http://www.cj.com
Kanoodle Brightads http://www.kanoodle.com/about/brightads.…
3. Sell advertising for your site directly. This is admittedly a more difficult route for a small business site wanting to earn advertising revenues. But hey, as they say: “no pain, no gain!”
4. Affiliate Programs – you sell other people’s products that your audience may be interested in; and you get a certain commission after the desired action was done (whether a sale, a lead, subscription to email newsletter, or however this is defined)