Plenty of good information to find here.
Mother Goose, that's a nice idea.
SlyBaldGuy is right too - content is king.
The lesson I learned is that a forum takes time. Time to get going (if ever

) and a lot of
your time. It is at least as time consuming as running a website at least in the beginning. I have seen many people starting one just because a website must have a forum and don't give it more thoughts or time. The results are dead boards often spammed to death ..
My advice would be - only offer and run a forum if you have the time to maintain it and most important to build up the community.
Then check out other boards with the same subject (e.g. a tv show or football etc.) and compare - if they are successful (and the number of members alone is not that important - look at the number of posts per day) what do they offer. Which content are must-haves, what would work for your own board, what can be found on every board so it is completely boring to have it too and what would be new and interesting for users.
Something else I would think about - the use of board speech. It is quite difficult to find a balance here because some board-lingo creates a feeling of community but newbies or potential users will not spend a long time looking at a forum and decide whether they like it or not - if they get the feeling they can't navigate there, don't understand the category names etc. they will probably leave.
E.g. if the category titles in a Star Trek board are allusions to episode titles it can still be confusing for a new member or a potential member to e.g. find out where to find news. On the other hand, just naming the categories "news", "episode discussion" etc. is a bit boring and will not distinguish your board from other Star Trek ones or the zillions others.
Another difficult thing which however should be decided in the beginning is how strict you want to rule your board - every forum has rules and lawbreakers will face consequences but it is up to you to decide how much a rule can be bent.
Example: if you have the rule that chat or sms style is not welcome in posts you will not only have quite some work in watching over posts, you will also have to decide what is sms or chat style and what not.
I have also seen people begging strangers to become mods in their forums - this is so pathetic. I strongly recommend to pick moderators (if you really need them) from your own community - usually becoming a moderator is a kind of big reward but these people should also understand that they have new obligations too with that "promotion".