Annealling the metal before shaping or after a lot of working to prevent the metal from cracking. The methods are varies, but essentially, one heats the metal, then cools it very slowly. The metal will then regain its softness and can be worked. Afterwards, the metal can be tempered, or heated and cooled quickly (as by quenching) to regain durability.
I think if you investigate the forums used by jewelry fabricators (those that make jewelry from ingots, sheet, and/or rod--you might try the ganoksin orchid forum archives in fact) you'll be able to find the best methods for tempering and annealing for the size, shape, thickness, and alloy of brass you are using, plus how to remove or prevent fire scale and how best to polish it (e.g., a brushed finish, mirror polish, and everything in between).