It depends, really.
I used to complain to myself why my forum grew very, very slowly in the beginning. Well, every beginning is usually slow, but then I realized that the niche of my forum is unique that not many people seem to know. That makes advertising, especially in sites like this, didn't yield a very good result. I'll be honest, from lots of advertising forums I've been to, I don't think I got that much results except that being noticed at Google slightly better, I suppose.
I also learned that the best way to advertise is by knowing the circle of your niche. For example, for advertising forums like this, it would be best if you advertise it in other advertising forums like FM. In case of my forum which is a music forum, it would be great if you visit music sites, leave a comment and link to your site, or utilize social networks, telling friends, and such. Get to know audience which may like your genre, that's the correct way of advertising.
As for staying loyal, we can't deny that there is a moment in each admin's life where it's at the lowest; you feel bored and tired doing your work. That happens to me once in a while, At such time I would pull myself back a bit, calm down, and look into other sites, thinking of what I can and should do for my own forum. That's usually how I get my motivation again.