For traffic SMO and blogging are the best technique. Have a blog write useful articles and shared it among your followers. SMO is by default a proven technique to improve traffic and blog too increase the traffic of one's website by 20 percent.
I do search engine optimize my website to receive traffic from the search engines like google, yahoo, bing etc. And some times i do spend some amounts on PPC advertising. However, SEO (search engine optimization) is the recommended marketing way, tactic for any website.
Social Media Optimization is the best one. rest is Forums Posting, Social Bookmarking and Local business Listing is the other ways to Get local traffic
Do you ever know Linkedin dot com. If your niches are fit with kind of groups over there its piece of cake to get a lot of frees traffic. Trust me
It depends on the type of traffic you want and how fast you want it. If you want to see instant increase for your traffic, I suggest AdWords. The disadvange is that, the moment you stop the AdWords campaign, you traffic will decrease. But if you want domain authority along with increased traffic, SEO is the option, which starts with the most important aspect: your website. This means on page optimization. There are a lot of SEO guides out there, and after consulting them and making sure your website is well optimized and has at great content, then you should start the off-page optimization - creating backlinks from high PR websites (.edu and .gov are more efficient), article submission, social bookmarking, social media, etc.
I would go for social-media if I were you. Very target traffic and solid conversion rates. After all they don't cost too much and they are pretty targeted.
I've been using free advertising sites but this is time-consuming and doesn't seem to draw traffic. It does help with link building but I'm not sure I would suggest it. Forums work well if you have experience in the products you are promoting.