Its easy all you got to do is
1: try to update the server as soon as the update comes out so people dont go looking for a differnent server and forget about yours
2:mod your server! everyone loves a modded server
3:make it so people can buy creative or buy fly
4: add arenas such as mob arena
5:add parkour
6: make different worlds (maybe a skyblock world?)
7:take out creepers explosions but keep tnt explosion
Try to follow these steps and your server should be popular for a while please diamond and please comment :P :)