Location: In a state of confusion
And I'll just add that the best traffic is organic so it goes back to what others are saying here as far as having a good strong knowledge of the subject matter. Establishing yourself as a good, reliable source and willing to help. You've got to have that and you've got to spread your knowledge all over the place.
Are there enough interesting things to talk about regarding this subject?
Know and understand who your target audience is and when I say understand them, I mean you really need to know what interests or intrigues them.
Do you make posts on the forum that engage people to want to respond?
Do you Interview experts and post the interviews? Could be short blogs or videos with Q & A advice.
Post your own advice - short blog posts on other sites related to your forum subject. Then post the link to your forum under it (if allowed)
The key is to engage people enough to want to go to your forum to see more, voice their own opinions. You might want to consider doing a weekly blog with links to the forum for commenting.
SEO is important but you really need to build a good reputation and both of those take time. Be patient, be wise and persevere!
If this doesn't work then perhaps you should think about expanding the subject.
I wish we were better strangers....
I'll always cherish the original misconception I had of you.