Blowing the dirt out with a puffer or canned air is better than nothing, though may accomplish next to nothing . . .
The outer rotating case of the motor is lined with strong neodymium (rare earth) magnets. If you've ever put a magnet in sand, you'll be familiar with the black iron filings that cling to it. If you get this stuff in the motor, a puff of air will not clean it out. A strong blast of compressed air may not either, as there's no good straight path in and out of the motor without disassembly, doable, but not recommended without a small puller. (I took one apart and the bearing to shaft fit is almost an interference fit.
Best avoid the problem by using a pad for take off and landing if operating off dirt or sand.