The trick to running any server is to either do what the players want or do a thing and recruit players that want to do that thing.

If your server is dying, you need to find out WHY? Ask the players and decide if you can fix their problem as the host. Sometimes it's best to switch gears, sometimes you need to find different/more players.

In general to keep players you need to keep them engaged.

When I play with actual friends, I play how they like so they enjoy the time and are likely to play again. Sometimes it's persistent creative with strict themes, other times we might run a bunch of pvp mini games.

As a host you can always be more involved. Having a set event day works well if you can commit and plan. I would host fishing tournaments every Sunday morning. They were dead some weeks but other times everyone would show up. But the important thing is that everyone knew of they showed up on Sunday morning they could fish and win prizes. Doesn't matter what you do (scavenger hunts, pvp, racing), but advertise it and do it on a schedule.