New picks or when picks get scratchy. I polish all of my picks with a dremel tool, cloth wheel and red jewelers rouge. Takes the rough edge off of plastic picks, use care, very light touch. Metal picks, buff rough edges and outer surfaces, shine like a mirror. Only takes a few seconds.
To second Simonslick...the leather strap. I think Earl talked about doing that in his book also.
'Blocking first string.' 8 min