You should learn what steemmonsters is doing because it is also jumbo size project.
- You need to draw attention from a huge SP holder.
- Create an upvote bot that upvote using the some specific tag like #chibera.
- Make contests and ask them to share your contest.
- Giving some incentive to the steemians who play your game(You may already did).
- Make some story contest and let the steemian write.
- Public your demo of game to public.
- Invite steemian who has a lots of follower and ask them write about your game.