If you are able to get the Qatar National Bank First Platinum MasterCard, that's probably the best earnings rate -- I think 1 mile per QAR 5 (about USD 1.4) spent.

Other banks in Qatar offer mileage cards on and off, and it's also possible to get an American Express, but I am not sure if they are a QR partner.

There are frequently sign-up and other bonuses, however, so you'll have to explore the offers when you get to the country. Here is a link.