Basically:

1. Make your game look way better than it is
2. Advertise to millions
3. Hope thousands download
4. Even if those thousands quit almost immediately, you still got to show them 1 or 2 ads.

Here's a video of two people talking about how their pretty hilarious journey of how they did something similar as a joke and accidentally ended up making quite a bit of money: https://youtu.be/E8Lhqri8tZk (seriously worth the watch)