Visitors will not sign up if they do not see activity first. New forums are especially vulnerable to failure because of this. To prevent this from happening, you could try creating multiple accounts yourself and getting your friends to do the same in order to make it seem like there are more members and more discussion. Alternatives to this are hiring a paid-posting service, promoting your forum on other forums, blogs, and social networks, or simply finding more friends.

Also, try to get original content AND members with unique personalities, posting styles, and opinions. Cookie-cutter members and discussions are going to drive visitors away. A "rate the signature of the person above you" thread, for example, won't compel anyone to join.