In no particular order - remain calm whilst they wibble, up to and including a medicinal slap if needed, carry things, double check their packing/transition checklists, be out on the course wherever you can to yell supportive if not necessary true things, and be in the finish chute with a camera and a cold beer. Avoid Pirates, or you'll find yourself signed up and looking for a sherpa next year 
The one time I've sherpa'd, for a friend doing Blenheim sprint, I think I was more nervous than he was!