I have no experience with managing forums, but I have this question... How do forums get traffic when they first start out, or how do they start from zero? I ask because I've never seen ads promoting a forum before (i'm no saying they don't exist, it's just that I've never seen one). If a forum is starting out, how do they do to get their first members, posts and visitors?
It's hard to start a forum and growth is never normally a straight line - much harder. Many people will hire a bunch of people to create conversations in order to give a forum a healthy vibe because one sure fire way to stunt growth is to give the impression that a question will go unanswered for days if at all.
Forums do have advertisements all over the internet, however it's not easy to run a forum, you need time and dedication, your best bet would be to invest into adsense or look into advertising on forums in your niche. You should also try and obtain your desired keywords within Search Engines, especially Google, they really help, you might find this article interesting - Getting a high google rank using anchor text. Good luck!
Do Backlinks on do follow blogs and forums to get higher in serps and get targeted traffic. Also from my expierence do less competion keywords. I went for hard words like forum and boards i ranked but not very well. Easier to do less competive keywords. its what i'm working on now instead. Create 20-25 accounts start posting create a buzz. Sucks talking to yourself but before long members start to come in. Do phpbb its free then if you want to later after your forum has grown buy the other ones but i like phpbb myself hated it at first but now love it.
One way is being very active on a given forum that has a similar audience that you want to also drive to your site. Add the forum link to your signature on that forum and start participating (a lot). If people like you, they will visit your site.