I've had good luck using a Vibratory Tumbler.
I bought a large one years ago for polishing motorcycle parts, now I use it for coins, tokens etc.
If they're really dark and oxidized, the ceramic stones will cut that pretty quickly, but don't leave them for too long. Maybe 30 minutes or less.
Then to shine and buff, I use crushed walnut shells.
Run them for 24 to 48 hours, or until the desired finish is achieved.
I did a batch of early Wheat Pennies for an antique Trade Simulator using only the walnut shells and they came out beautiful. Nice shine and smooth finish.
All of this can be purchased at Harbor Freight.
I'd like to find some old brass dollar tokens and clean them up.
Hope this helped. And the other suggestions aren't bad ones, just take a little more effort.
Curtis ash100