Qualifications
You need to know how to operate a Zamboni—big shocker, right? You'll also have to be strong enough to steer the machine around the ice—and the thing is big and heavy, so it's not easy (especially if you're against the boards).
It takes some people years to learn how to properly operate a Zamboni, while others pick it up rather quickly. It really depends on the quality of the rink you're working at, and if you're working games, public sessions, or freestyle figure skating sessions. All ice is not created equal, so you'll also need to know the difference between cutting the ice for hockey and cutting it for figure skating.
Understanding the ice and what makes a good cut is as important as knowing how to operate the machine.