I've a android app with 8200+ active users..
I already tried ads.. the amount generated by it was low..
I tried ads + premium, the Google fee is very big and makes the app expensive after their fees, so it wasn't that good too.
Right now i removed all the ads and premium and added a simple donation button, until now (1 month) i got 10 donations from 8200 users.
I don't know what to do more.