My 2 cents

Having a well thought out idea that is formatted easily enough to sift through. Do people see what it is, understand what it's about and do they then want to actually join. The less effort to join the more people will flock to it. I'll just add that those that do join with medium effort applied usually stick around as they have more value put into their characters. Always being open helps me get a few inquires about joining which keeps the fresh feel going I guess. Some do actually join and that helps a lot with the character stagnation, seeing the same characters over and over can get stale.