So, I can go over my theories of what will and won't work and some of them might even be right, but I figured I would use a real example rather then conjecture.
Back in may/june of 2015, I logged in to coa for the first time in almost 3 years. It was 5 pmish my time and there were 6 people on. 5 pm my time (new york baby!) is the gateway time between the euros and the americans, and is traditionally the most populated the time the server sees. So, needless to say, I was a bit disappointed.
But, I went through the time to get logged in, figured I would poke around a bit. Ran into a guy named goatman (that was his login, can't remember the characters name), and the two of us started jamming quests. I made a comment about it being a bad day, and he said "6 people on, thats a good day!". Somewhat deflating, but I was having fun running through some of the old quests from my heyday so fuck it.
Next thing you know, we had a few people joining our group. Now personalities are starting to come out, people are getting into the rp, and we are questing away, having a good time. The next day, our group grew by one or two more. Three days later, we were worried about the max amount quests would allow, and there were ten people on at the same time goatman had said it was great to have six.
Within a week, out of nowhere, another old face appeared. This time on the DM side. Now, I have a theory that polaris secretly has a crush on me and is my internet stalker, but since its still just a theory we will for the sake of this story call it just a coincidence. wink wink.
So, now we have 10-12 people logging in, a dm that goes nuts for his first few months back like clockwork, and the server feels alive. Pol makes a few posts on the forums, says a few things on irc to get people in game, and now we are up to 15 people less then three weeks from when it was exciting to have six. A week later, PDs are coming back, and its time to hide your wife and kids. Moloch hath returned as well. For almost an entire summer from about 5 pm my time to around 10 pm, we were hitting 25 people. We had a cool plot, and stuff. The server was alive once again, in just a few short weeks.
Now, things changed fast again. Plots ended, players went back to school or whatever, and DMs while enjoying their short burst of energy over the summer were people who had been there done that before and that will always lead to faster burnout the second time. That's when I was asked to join the team. In my two years, we had lulls, and we had high points. I came two away from 40 people on for one of my events, still a point of pride.
Now, you may be asking, is there a point to this or is LaF just on another rant about how awesome he is? And the answer is yes, to both. I am awesome, and the point is that logging in and having fun, and taking the time to spread that fun around, is the key to getting the server back to where it was just a short while ago. More DMs, more players, more plots, more player driven stuff, ect ect ect...these are all just pieces of the big puzzle, but the point has always been and likely always will be one thing. Have fun.