Rule 1: Keep them out of direct light.
Rule 2: Don't give them water, not even to drink.
Rule 3: And most importantly, do NOT feed them after midnight.
If you're thinking this sounds more like the set up to a horror/thriller flick, you're right. Spielberg's 1984 Gremlins smashed ideas of what holiday movies were supposed to be. As much fun as Gremlins is, it also has a strong anti-colonialism theme. Billy's father essentially steals Gizmo while traveling because he thinks the creature would make an awesome gift for his kid. At the end, Mr. Wing arrives to take Gizmo back, telling Mr. Peltzer that he had no business taking him in the first place. Nothing like a side of truth to balance of Christmas dinner, amiright?