Onsite Staff and Moderators
Your staff and moderators make up a very important part of your "customer service" team and, therefore, must be picked carefully. Make sure that your staff is specialized in the areas on the site that they are responsible for, and make sure they have good people skills. Establish guidelines about how often they are expected to be online and/or helping visitors. A good representation can make the difference between a large group of regular visitors and a large member base of which very few people actually visit your site and take part in regular discussions.
If you do not have the luxury of actually hiring people to supervise the site with you, don't make the mistake of simply accepting anyone who send you an e-mail to do moderating for you. Find out more about the person's attitude and category-related skills by checking his or her previous posts on your forums (by my own experience, this is where most of your would-be moderators will find you). As with virtually all (initially nonprofit-based) Web sites, you will probably be able to hire moderators later, after your site has grown in size and popularity.