here's what i've found as someone who supports forums.. in other word i don't go out and make my own forums, but come in to help peeps with THEIRS..

the #1 is that the owner (and staff too, but mostly owner) needs to have both a passion for and a keen understanding of the main forums thrust..

if the forum is all about fishing, the member #2 admin should be a passionate fisherman

if it's all about german shepherds, then be an owner of one and know all the ins/outs..

lawnmower equipment

hunting / trapping

camping

simulations / gameplay

etc etc...

each 'niche' or subject needs to be something you know a lot about and are passionate about...

This attitude spills over into the forums.. the new members will sense that... it builds from there..

But to just pick a 'nice subject' and hope it takes off because it's unique won't work if you aren't totally into it..

The effects are synergistic from that point on, from what i've seen... you find a handful of very good members who become part of the staff and let the forum slowly grow from there..