MILEScredits are pretty cool, and there are several ways to get more of them.
You can use your "Refer a Friend" code to encourage people to join MILES. This way, both of you get 10€ MILEScredits. This happens automatically once the person is verified. You can find the code in the login area.
Or you can refuel cars with a level below 25%. For this, you get 5€ MILEScredits. The booking for this is done about once a week, so don't be surprised if the MILEScredits are not booked directly after the trip.
On our Facebook page we also raffle tickets for interesting events, and usually there are also some MILEScredits involved.