Know your users. Know what they like, hate and love. Know what will inflame debate and know what will turn them off. Know those who will be pivotal in your forums future. Promote them accordingly.
If you see a forum as simply a business venture you’ll struggle to succeed. You need to delve deep and interact with everyone for it to work properly.
If you have a bad memory, keep a spreadsheet of all of your users and note personality traits. Note who they are friends and enemies with. This may sound like its overdoing it but if you have a complete profile of your userbase youll be in a position to create topics on your forum that generate a reaction!