Here’s a few things I do whenever I set up a new forum, and a few I don’t but that are available.. Some of it is more search engine orientated than people… but it might help.
- Change User Titles (Use keywords .. Slots newbie.. Casino Champion.. whatever
- Join a posting group
- Pay for Posters
- Seek out talkative folks, as honorary moderators
- keyword all catergories and forum names
- post a few articles in the forum
- Use controversy
- Use your network
Changing the user titles to keyworded items means those keywords are going to be all over the place, and gives your forum another shot in the search engines, I didn’t use my own examples, because well that would just be dumb.. but be creative, choose some keywords and make use of them.
I and my partner run a little posting group, I used to be a member of one on google that went dormant so we created our own. There may be others, beats me, basically we all just promise 2 posts a week on the other guys forums .. in exchange for posts to ours.
There are sites that offer this service, as well as CAP members willing to do it (please don’t pm me and ask, im out of this business, and suck @ saying no:P ) .. you might try an ad in the services and content are if you want to hire, better to find them here so they know what theyre talking about 
Giving ppl the title moderator, with few privaledges is 1 way to get some spam removed for free, as well as make your users feel special, so they will return as well as promote your forum.
Writing articles and plopping them into the forum doesn’t generally spark much discussion, but it does add some keyword value. If you end up with a great useful article on your forum that you think the masses must see, add it to http://www.digg.com and other like sites (stumble – delicious.. etc) that will bring some traffic, and likely some users.
Sign up with an alternate user name, and use controversary to your example.. Take the unpopular road, people like to debate. Gives them a reason to talk, and u can bet they’ll be back to see if the idiot responded to their post yet.
Use your network… I have a network of close friends that help me in just about every adventure in my life, both offline (the MSN group 
(Heya guys!! lol) and offline.. ppl i share interests with etc.. Be there for them, they’ll be there for you. Get them onto your forum chatting, if they own one.. do the same
Hope there’s at least one useful hint here 
~LadyH