The forum could use a different template, a bit more stylish could do no harm. Dont do subforums mostly those are not very appealing.

For the rest, not too much adds (none would be best? , if you need extra cash for the bandwith on the server, add a paypal button, i think many ppl wouldnt mind in donating a few bucks to help you uphold the server).

I love to take curse.com as an example, dont go to flashy, they killed the site with all the gui candy over there.