...put in some serious elbow grease. Dedication, perseverance, and always keep the faith. In short, you're most likely to success if you put in the hard work. Plain and simple.
Consider a community in your life that you deem to be successful. Maybe it's your book club, PTA, church, running club, ladies lunching, whatever. Now think of how that club got started, and who is behind it. Who is always sending emails, making phone calls, showing up, and evangelizing. Whoever that is, that's most likely your community manager, even if said person doesn't carry a formal title. This person is the engine and is putting in some serious effort to keep things moving as they are.
What if that person left? Got sick? Had a baby? Went to graduate school? Unless those reigns were turned over to someone else, most likely, things would start to dissolve, even if just bit by bit. First the emails stop coming. The events stop being planned. The harassing encouraging to show up to events dwindles and people opt to stay at home. Just like people like to jump on the community train that is moving at full speed (because they know they are part of something real), people fall off when they sense a community is starting down the path of demise. They get fewer responses to their questions/comments/ideas (and we all know people LOVE the anticipation of getting responses).
So in order for your community to thrive, there needs to be at least one person chugging at all times. Someone really passionate who will spur conversation, go find new members and bring in lost old ones, organize events, and essentially keep the fire stoked. It needs to be steady and consistent.
Online Community Management works exactly the same way.
Here's an analogy -> Community Management as Stoking your Cold Winter's Night Fire
It's nearing wintertime. If you happen to have a fireplace in your living room, and ever tried to make a fire, you know what that process is like. First you put in the large logs that will be the real sustain-ers. Then you put in the twisted up newspaper to allow the match to catch really quickly and get the initial flames going. Then you put in some smaller logs and twigs, maybe as a half-way point between large logs and easy to catch newspaper. Now get that fire going and see what happens. Often, the newspaper burns up immediately and slightly catches to a few of the other logs. Over time, you may have to add more kindle wood, newspaper here and there, but essentially it's a lot of work and needs tending to. If there's no source of fuel, your fire is guaranteed going out just as fast as it started.