Opinions vary widely on this, but an old timer gave me this piece of advice when I picked up my 8mm Mauser (it has only eaten about 600-800 rounds of corrosive ammo since then, with no ill-effects):
Easy route:
Buy a bottle of black powder cleaner... This stuff looks like skim milk, and appears water-based rather than oil based (I'm guessing it is modified soapy water). Run a patch through your gun when you finish shooting, along with a light coat of oil.
When you get home, strip the gun, and use more of the blackpowder cleaner. Dry the weapon/parts, and then clean like you would a normal firearm (patches, solvent, bore brush, patches, patches, patches, maybe a light coat of oil, more patches).
I've been doing that for years, and my Mauser still shines like it did when it was new... And all I use is corrosive ammo at this time!