Tips I used when starting off..
1, Content, ensure you have regular new content
2. Keep the number of forums to a minimum until you have traffic to populate them with content
3. Controversy- everyone likes a small disagreement/debate/arguement, one devious trick is to create your own "discussion" using two usernames, as people start to join in let one drop away
4. be "Niche" just creating a set of general forums in the hope of attracting everyone will only put you up against the Big Boys with lots of cash to spend on marketing,
5. Have a clear set of rules of what is permitted, and what actions will be taken against users if they transgress
6.
Keep at it, my forums started 7 years ago, it took me 3 years to build up any sort of traffic, a further 3 years before anyone in the niche industry took much notice of it, last year I sold it to a major publishing house and now get paid to babysit it

7. keep your expectations of traffic reasonable, in the first year I was pleased to have 100 registered members of which 25 were regular posters, this year, despite changing boards in year 4 and losing many registered members(couldnt afford to get the database converted at the time), we have just under 7000 members and do about 6.5 million page views a year