A few things to note:
Make sure your server has voting sites with good rewards. Push your players to vote, offer xp drops if 5 players vote or whatever.
The exact place that you spawn is highly important. If you spawn next to a bunch of signs or some kind of quiz you most go through to join the server, most players will leave. Make it easy for players to start playing right away.
The good thing about the voting sites is that if players like it, they stay on and vote. As long as your server is fun it will grow through them. For example, my server got to a player base of 20 within one month, no paid advertising.
