For rifle brass, I swipe left index finger over open can of Imperial sizing die wax, smear over case with left index finger and thumb while rotating case with right hand and inspecting for defects. Then scrape teh case mouthaccross my left thumb to get just a little on the inside edge.
Size away...
Never had a stuck case yet.
For pistol brass with carbide dies, I do the same as above, but only lube every tenth case or so. This makes the press stroke on tapered wall pistol brass (i.e. 9x19) with MUCH less effort.