It would be good to implement MISSIONS with npcs with rewards, how to deliver a Pokémon with 31 iv in speed and that they reward you for that, obviously, that it is from the trainer and not buying the pokemon, how to also implement ACHIEVEMENTS that are or are not with rewards as well. It could be built up to some sort of TRAINER LEVEL based on your achievements or something like that.
Continuing with the missions, it could be weekly or monthly, as I explained, it could be to deliver a special poke or also battles, or find something, like a treasure and mix those things. These missions could give the experience to implement a trainer level and thus, it is a matter of analyzing it well, but I think the basic concepts are understood.