Before you can start a forum, you have to come up with a niche.

This is the main topic your forum will be about.

I'm a member of various webmaster or forum related forums. And I often see posts there from people that want ideas to create a forum about.

Of course it's a good idea to get some ideas.

But you have to keep in mind that those people probably know nothing about you …

They do not know what you like, what you dislike,