Look for a cloth. Anything that is soft and absorbent and won't leave threads or lint behind is suitable (part of an old t-shirt, for example). I use a Flute Flag, which can be gotten through fluteworld.com, and does an excellent job. Don't use paper towels. They will leave behind paper "lint" (don't rightly know what to call it), can be quite rough, and if they absorb too much could dissolve, leaving a layer of moist paper behind.

I clean mine off with a satin cloth.