Forum Moderators: mack
Provide useful, quality content which people want to read, will bookmark and tell their friends about. Become an authority on your subject and get good backlinks from respected sites.
If you buy traffic through AdWords and don't have quality landing pages, then expect to pay a lot of money for this method. Also expect that other 1st tier programs will adopt similar policies in the future. If you go with 2nd or 3rd tier PPC programs, don't expect the wuality of the traffic to be very good.
So your best bet is to follow what has already been suggested- build a site that people want to come/link to. The links and traffic will follow.