Cut out, and punch holes around edge, 1/4 inch apart and 1/4 inch from the edge. Try on sweater, and pin patch in place. ("You want to see exactly where your elbow is," Katie says. "It's oddly not very easy to just eyeball it.")
Hand-sew in place through holes.
Micropunch (at craft stores)
Needle and embroidery floss or craft thread
Blueprint elbow patch template
A bright color is a modern tweak to the tweedy college professor's elbow patch -- all you need is a scrap.