The only advice I can give you is to POST POST POST yourself! I say this a real lot, but I might as well just repeat myself here, at the chance of being repetitive. Members are selfish. They only care that what they have to post gets seen and replied to. So the goal to turning an inactive forum into an active one is to make sure that you instantly reply to every thread or post that is made. One member at a time will see that THEIR own post has been answered right away, and so they'll come back. Don't worry right away about getting conversation going. That will come with time. At first, just focus on making sure that YOU personally answer every single post made within a short amount of time.

I am not a fan of giving members prizes in exchange for posting. What ends up happening is your members only end up spending time on your site because they want what you're giving away for free, and they don't really care about the site at all. As soon as the well runs dry, or you can no longer afford to constantly supply members with free gifts everyday, they'll all quickly leave and you'll be back to square one.

Contests are a really good idea and can be used to improve the community aspects of the site. However, contests should encourage members to participate more and bond and encourage community - not give them a reason to be on your site during the here and now when they really don't care about it at all.

That's a very general question, and that really depends on you.

I have a forum with about 300 members, and the forum hasn't yet come to a state that can grow alone.
But for instance I meat today a guy that made a forum with 250 members in 12 hours!

i have waited months and paid heaps of advertising and only have 16 members

I'm a strong advocate that a website can never truly be self sufficient. Comments?