Hold a contest? Put sociable links on first posts in threads? Put your forum URL in your email sig line. Hire forum posters to post stuff to your forum then quote their posts in posts to other forums. Hold a contest. There's so many ways to go about boosting your traffic. Most methods are free.
You should read as much as you can. Read this forum and others like it. See what people are saying works and what doesn't work. Then you should ask specific questions about specific practices that you don't understand. Asking for a general blueprint to success will not get you the help you are looking for. Online marketing takes effort. Part of that effort is learning. Don't expect others to do the work for you.