Dry, and de-greased threads.
A brake, is an entirely different animal from a flash hider.
Flash hiders have exit holes you can drive a semi though.
Brakes, typically are .030-.040 overbore- meaning you have fifteen to twenty thousandths of an inch clearance around the bullet as it exits the bore.
Threads must be perfectly concentric to the bore, and if being tightened to a shoulder about 30-40 ft lbs of torque to keep it tight (that's TIGHT). If using a crush washer, wherever it needs to be timed correctly.
I use high-temp (red) loctite- many use Rocksett, which requires even higher temps to remove. If you do not use any form of threadlocker you need to frequently check the brake to be sure it has not loosened.