I prepped a mold on Tuesday.
Basically, use some sort of cleaner to get the milling oil off, then add a thin layer of carbon to help the bullets drop free.
I accomplished this with some spray brake cleaner and a few matches. Yesterday, I ditched the matches for Frankford Arsenal's Drop Out Bullet Mold Release Agent. It's much easier and ensures complete coverage.
Once I got my mold to optimal temps, brand new cast beauties dropped right out even without shaking.