DO NOT touch the rosin or the bow hair while following these instructions. Doing so will cause oils from your hands to stick to the bow hair which will deteriorate the bow hair quicker.
Before applying rosin, tighten the bow hairs by gently turning the tension screw at the end of the bow. Avoid making the bow hairs too taut---the separation between the bow stick and hair should be about the width of a pencil.
Place the bow hairs flat on the rosin at the "frog" of the bow (near the bottom where the tension screw is), and gently rub the bow hairs up and down a few times (as if scrubbing a small spot on the floor).
Then, draw the bow hairs straight across the rosin until the tip of the bow is reached. Repeat the same gentle scrubbing motion at the tip of the bow, and pull the flat bow hairs back to the frog again.
Do this several times so that the bow becomes thoroughly coated with rosin.
After playing, use a soft, dry cloth to remove rosin dust from the strings, body of the instrument, and underside of the viola bow.
Watch the video below for more help rosining your bow: