Just be unique and get a domain name (TLD one) if your going for a large member base. Just post regulary and don't open your forum with no topics or posts, wrong permissions and to many boards. Then just advertise and advertise 🙂.
I would also recommend gathering up another one or two people to be your staff. I suggest someone who you may already know. You definitely need a good staff to begin, not necessarily the amount of staff members. Another important thing to remember for a small forum is that don't promote people to higher positions such as staff for minimal reasons. be sure about who you're going to be promoting and whether you can trust them. Trust is key amongst staff, and it has to be maintained.