Forget the stoopid (my opinion) dryer sheets. They are a waste of time. Urban myth, and all like that. People get excited when they see the sheets getting grungy, but overall, they do not really CLEAN the media much at all.
Put the mineral spirits and polish in BEFORE adding any brass. Allow the polish/mineral spirits to vibrate without any brass for about 20 minutes to disperse the liquids in the media. Then, you can add brass.
Remember that it's not just the media pressing against the brass that makes it shiny. It's the brass pressing the media into the brass that makes it go better. So, I always empty the media from the tumbler, add brass, and then re-ad the media on top of the brass. You'll find that you can get more brass and more media in that way.
Oh, and when you run out of the expensive polish that they give you with the tumbler, get yourself some NuFinish liquid car polish, and use a capful of that from time to time.