On the Peak
Never leave injured, exhausted, or altitude-sick partners behind. At the very least, send an assistant down with them. Don’t let faster hikers take off, especially going down; attitudes tend to get casual, and hikers often get lost when they descend the wrong ridge or gully.
Carry a light rope (and know how to use it) on any steep peak, even if the route is only class II. Easy slopes get rain-slick, and people can freak out over exposure or wander off-route onto dangerous terrain.
Don’t be afraid to bark orders if hazards like lightning or steep terrain threaten. Groups can freeze up in iffy situations, and that’s when you need to take charge.