Be clever.
It's not all about having a chatbox, a gallery, a cool theme, a this, a that and another thing.
Stop for a second and think about what you can do that would make your forum unique and fun.
A lot of forums have chatbox's, gallerys and all kinds of cool stuff like that...so if your members get bored they can go somewhere else.
But if you make something unique and clever, then you're the only one that can provide the fun.