Not sure if this has been posted here before but this is an awesome list of the biggest forums online. This could be a goldmine if used properly. it's really simple. Just find forums related to your niche. Signup with your website link in your signature. Start posting quality material and building yourself (and consequently) your site in the community. Yeah i know it's no brainer stuff for most of us here but maybe this will help out some newbies...
Link: Big Board Forum Rankings
http://rankings.big-boards.com/?sort=members&filter=all,all&p=all
Link: Big Board Forum Rankings
http://rankings.big-boards.com/?sort=members&filter=all,all&p=all