Hawkgirl - 12:23 am on Sep 21, 2010 (gmt 0)
Hmm. Depending on how familiar you are with the software, I'd say a big "must" is to play with it for at least a few days until you're familiar with the user functionality and mod/admin functionality.
Initially, I'd leave everything at the default settings and then start turning things on and off to see how they change your forums. Some people like all of the bells and whistles, while other people like it as simple as possible.
Put some analytics on it so you can track what is being looked at.
Do you have the forums only or the full CMS suite? If you've got the CMS suite, a good investment of your time is to figure out how you want to structure your content before you start plugging it in. It is a hassle to go back and make changes to sections and categories - take it from someone who had switched the content architecture around three times. Hassle.
Visit vBulletin.org - lots of great mods and plugins. There are some great anti-spammer registration plugins - you'll want to get one of those ASAP.
And then it's going to depend on what you want to do with your forum. If it's a gaming site, there are tons of add-ons for gamerz. If it is a music site, there are ways to add media streaming. It's all based on what your target is.