Great ideas, everyone.
Another rule I enforce: Go down below facing backwards. This applies to everyone, regardless of the sea state. It is a steep ladder, and I don't need anyone falling.
On my boat, a center cockpit with a full enclosure, it is not obvious that there is a danger of being hit by the boom if you're beside the cockpit. I always explain to people that I am safe standing next to the enclosure, but if you're any taller than me, you won't be. I also ppint out a dangerous spot just aft of the cockpit, where the traveller is, across to the lifelines. One "unexpected maneuver" and someone could be hit by or swept overboard by the main sheet.
