Make some popular friends?
Actually, that's one good suggestion. The more links you have to your forum, the better (however, links like this one probably don't count for much, which is to say, if you're trying to use this to spam the boards, it's not likely to be effective). Another suggestion, with any forum, is to make sure you're specialized enough to be unique, though not so specialized as to limit your audience too much.
As far as the site itself goes, that theme is really difficult to read and sort through, so it makes me want to quickly go back or close the window. Get a more inviting theme and you'll find your visitors stay longer on average. Something not quite as dark (a background of a very dark gray instead of black I find makes things easier to read, and throw in some lighter areas).
Then just promote, promote, promote (without being annoying about it, that's a surefire way of killing a site).
jW