Assuming you mean the bolt carrier and bolt, there are two methods; mechanical and chemical.
The chemical method is to use a carbon remover liquid. A good one is Slip 2000 Carbon Killer.
All that's needed is to shake the jar well, soak the parts for about 15 minutes, then brush to finish with an M16 "toothbrush".
The mechanical methods use various types of scraper tools to scrape th carbon out.
Of the available tools, most people consider the C.A.T. M4 and the Magna-Matic, the best because each of these two do it all, where other tools require buying two tools, one for the carrier and one for the bolt.
Using either the chemical or mechanical method will clean the bolt and carrier fast and without lengthy soaking or brushing.