Implement a daily login bonus system. Every day you get a reward.
Non Roblox Premium users:
Day 1 - 5 Nova Bucks
Day 2 - 10 Nova Bucks
Day 3 - 20 Nova Bucks
Day 4 - 50 Nova Bucks
Day 5 - 75 Nova Bucks
Day 6 - 100 Nova Bucks
So on so fourth
Premkium Users:
Day 1 - 10 Nova Bucks
Day 2 - 20 Nova Bucks
Premium users basically get double.