Pick the tape up and hold it in your fingers from one end with the label facing up. Smack the tape hard against your other hand several times. Turn the tape upside down and smack this side several times.
Insert the tip of a pencil into one of the spools of the tape. Spin the pencil with your fingers to wind the tape all the way to one side of the tape. Insert the pencil into the other spool and wind the tape all the way to the other side.
Insert the cassette into a cassette player. Advance the tape to the end, then reverse it and advance the tape all the way to the other end. If the tape sticks and shuts off the machine, flip it over and go back. Then flip it again. Repeat winding and flipping the tape over until it runs smooth.