Do buy as many as you can afford (realistically about 20 is a good starting number...this prevents having to wash so often). Do assign MFs to certain tasks (some for wheels, some for paint, some for glass, etc.) Do wash them separately from other laundry (I like using a fragrance/dye free detergent). Do always keep a few around with some QD for unexpected problems on the road. Do buy from a quality vendor (CMA, PakShak, JT International, YoSteve, etc).
Don't use fabric softener. Don't dry your towels excessively (there's some debate as to the harmfulness of drying MFs in the dryer fully, but I don't take the chance). Don't try to rip the tags out (can screw up seams...cut them out instead). Don't use them after they've been dropped unless they are washed (hence the need for 20+ for klutzes like me).