Its a bit tough to promote and market a forum and even more tedious getting visitors to register. You should put yourself in your visitor's shoes and ask your self "why would I want to register here?" You should be able to offer something unique and helpful in your forum. Always make it a point also that there are active discussions so peolple visiting them will not see your forum as a dead zone.
Maybe you should try enticing your members with incentives, like a point system. This might help bring in new members and keeping your forum active. Best of luck buddy!
