The admin knows the niche well and has website management skills, there are members who create useful and interesting content, and dedicated staff. These are three things that, in my opinion, makes a forum great.
An effective forum should possess clear rules and guidelines, and it should also uphold respect and inclusiveness. Having members feeling special and liked will encourage their participation and contribution to the development of the given forums.
1. An admin with a vision of developing relationships with his or her members.
You need to befriend your members and your staff. That's how you turn them from regular members to loyal members who keep coming back. A community with loyal members is successful all the way around.
2. The forum needs to have content consistently contributed to it.
You don't have to post 100 topics a day. You just need to find your comfortable posting frequency and then consistently do it at a comfortable pace. This will let members and staff know what and when to expect new content on your forum. It's another way to build trust and have a successful community.
3. The forum needs to focus on engagement and stomp out anything toxic.
An argument or incident that turns into a dramatic event will being toxicity to your community. It can destroy relationships, turn people against each other, and cause complete and utter chaos. I see it all the time. Forum owners getting into it with other forum owners. Members getting into it with other members. It'll kill your forum in the end.
In my experience, the above is how I can see the answer to this great question! 🙂