Great question for any desert flyers!
Dirt, sand and other debris can get into your motors, fan, gimbal, and exhaust ducts. As a preflight, you can turn your motors slowly and feel for any grit, sand or other objects that might be causing friction. If you do get anything in your motors, best to turn the Mavic upside down and shake it out. You can also use a smaller vacuum to get it out. If you blow compressed air into the motor theres no place for the debris to go but further down into the motor and can jam it.
Keep the cooling fins on the bottom clear of debris so that theres no restriction on airflow. Look inside the rear air outlet ducts for any dirt or dust in there, and shake it out through the back, away from the cooling fan end. The last thing you want to do is get something stuck in the fan.
Theres no air filter on the Mavic, so its really up to you be the the air filter. Try not to take off from sandy or dusty areas, but if you do, get yourself a landing pad so that foreign objects wont get sucked into your bird in the first place.