Do events with fun stuff. FFA battle, Big CTF maps, Assault, Race ect. There must be passwordless enterance.
People who play randomly, going from server to server like that, love them. But unfortunately, someone who have played JJ2 alot hates them.

Whatever you do, don't do tourney/2v2CTF/3V3/ect tournament to attract new people. They might get annoyed, because there might be some really good people, and not so good people. *Points at self*