An important factor a game needs is Jobs. Jobs are tasks that NPCs assign you and you do the NPCs a favor. Here are the different types of jobs a player can be assigned:

-Giving materials (i.e. Give me 100 light shards)

-Craft me a weapon (i.e. Craft me a Sudaruska)

-Kill me monsters (i.e. Kill 20 dreadnaughts)

-Kill me rare monsters (i.e. Kill 3 soul jellies)

-Give me crystals (i.e. Give me 100 dark matter)

-Give me a heated equipment (i.e. Level 10 Swift Flourish)

-Show how you look with this outfit (i.e. Talk to the NPC while wearing a specific set of equipment)

-Buy me an accessory (i.e. Buy me a set of Prismatic Bent Vents)

-Buy me a costume (i.e. Buy me a Black Rose Regalia set)

-Win PvP games (i.e. Win 10 games of Lockdown or Blast Network, depends)

-Find this NPC (i.e. Find an NPC that the NPC who assigned you the job; hide and seek but with someone else)

Rewards will depend on your task. If you give the NPC a really rare item, expect an item you can't get anywhere else.
So, anymore ideas? Hope you liked this suggestion!