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Did someone say Adwords aren't expensive?
From my experience of making my living from my sites, you need to provide a product or service that is needed and valued. The site will eventually get busier through word of mouth, which in the internet age usually means a very nice post in a forum.
Advertising can be very expensive, particularly Google Adwords, though they do work very well in terms of getting visits. In my case I've never sold a product of high enough value to justify paying 50p UK per click. You can easily evaporate hundreds of pounds on Adwords, as I have done, but for me they weren't cost-effective, in fact I concluded they were a rip off and reminded myself never to use them again. Especially for charging a high price for very small niche search terms that no-one else was bidding on.
Traffic for traffic's sake is utterly pointless unless it's quality traffic, i.e. visitors who are actually interested in your product/service.
If you don't have a very large advertising budget, a good deal of patience is required!
One of the best things you can do is issue a press release. Completely free (if you do it yourself) and can result in very good quality visits to the site. In my case I got contacted by the editor of a magazine who got my press release and asked me to write an article, which I did, and which he published. The magazine was the top UK publication in the niche I was in. I got two or three glossy pages with some images and MOST IMPORTANTLY got my web address on the end of it. No charge.