You can get new players by announcing a new-update with great stuff on forums and have a giant celebration on the server. Make your updates balanced if you can, like one things favoring new players, and one thing favoring old ones. Like Giving new players a head-start to make them feel special- free money or a free kit. Then give something old players would like, like more storage for gear and a present for getting a certain amount of kills. After those changes, have small drop parties (No super O.P stuff) just like some golden apples, some vip gear, or just exp potions every Week. Then if you don't want stuff to be O.P then nerf some stuff, little stuff not giant things, little things to make sure no one gets super angry. Like Donators only get 1 golden apple for the donator thing, and there is a max limit of money so no one can stock pile and just buy diamond armor and get pv 4 after getting kills. There can only be a clan of a max of 3 so no one can just have 100 people in their clan.
Not all of these have to happen they're just suggestions to help grow the server