For hand polishing, I use a 1:1 mixture of dark cutting oil and "low odor" mineral spirits. I switched to the mineral spirits from kerosene because I got tired of the smell. The mixture is used to lubricate the abrasive paper or cloth and greatly increases the cutting life and puts a finer finish on the metal. I also trim an acid brush to fit inside a mason jar and store it right in the oil so it's always there when I need it.
Whenever I have to do any draw filing I use mold and die maker's stones to remove the file marks before switching to abrasive paper. Start with 180 then move to 240 and 320 grit stones. The stones won't round off corners and leave a nice finish that only needs to be brightened up to your desired level of polish.
For holding odd shapes pieces that are being polished, I use a product called Thermo-Loc from GRS Tools. It's a plastic material that can be used to form holding fixtures. Just heat it in a microwave or with a heat gun and mold it to the part. Once it has cooled, clamp it in the vise and work away. It doesn't stick to metal so when you're done, it pops right off the piece. The best part is that it can be used over and over so a small package will last a lifetime.

Brownells Gunsmith Kinks® - July 2009