Once you get the forum designed and functioning well the next step is to get some activity and start developing interest. Go to
www.rentatroll.com and hire at least a dozen trolls to get the ball rolling. Hire them to spam similar forums with your url and start posting hyped bullshit threads to peak the surfer interests. Make sure to hire a drama troll once the activity starts as you want to keep the interest going.
After you have it running and growing each day, you need to then hire Juicy to come in for the kill. His barrage of funny pic posting and hundreds of daily useless threads will create even more interest and you've got yourself one popular forum. Then you can start selling ad space and bring in the "would you hit it" troll to post nude pics and keep the posters active.