Gather beta from guidebooks, topo maps, and trip reports on sites like summitpost.org, peakbagger.com, 14ers.com, and, of course, backpacker.com. Check current snow levels and trail conditions with rangers or local guides just before you leave.
Distribute equipment lists well in advance and require helmets on steep peaks (large groups generate their own rockfall). At the trailhead, ensure that everyone has high-energy snacks, plenty of water, proper footwear, and extra insulating layers.
Control summit fever before it starts. Make sure everyone understands that you won’t top out if conditions are unsafe. Plan a firm group turnaround time, and have a backup destination, such as a lake or a waterfall, ready in case weather forces you to bail.