As for the process: The visitor should have a extended visit visa in Qatar, the passport should not be near expiry (6 months), The visitor should pay a fees of 100riyals (not sure) for a re-entry visa before leaving for umrah - this will help in re-entering Qatar without any problem.

Apply for Umrah visa to the tour operators check for lowest price offering you need a white background photo, xerox copy of passport as well as the original passport to be submitted, you will need to take vaccination before you leave to umrah; from mesaimeer health center.
If going by your own vehicle: the vehicle should be in your name without any fines (you may have to clear all the fines before leaving or at the border).

Thats it! I hope i answered your question.