The side of all boxcalls should be wiped clean with a dry cloth, only. The paddle/lid should be chalked lightly and re-chalked only as needed and lightly sanded with medium sandpaper only when re-chalking dosen't restore the call to desided pitch.
If lid is sanded, lightly sand the entire length of the lid, with the grain, and only with enough strokes to remove the "shine" from the lid.

BTW: The only chalk I use is the Burnt Orange colored Boxcall Chalk by HS Strut.