After an accident, adrenalin is rushing and nobody thinks straight. It’s easy to do something which compounds the problem.
1) Ensure everyone is safe. If on the trail, move to an area where other trail users can pass. If on a road, move to the side of the road away from traffic but still visible. Put on an extra layer of clothing, as you will most likely be stopped for several minutes.
2) Fix broken people before fixing broken bikes. Even minor wounds can be nastier than they first appear. Use your resources to bandage, splint or warm an individual before using them to repair a bike.
3) Take stock of everything that is broken on the bike. After a crash, several things may be askew, bent or just plain missing. There is no point fixing a broken saddle if a wheel is tacoed beyond repair. It wastes time and resources.
4) Identify what resources are available. Find out what spares and tools every member of the party is carrying. Make everyone check, rather than just telling you; someone may have forgotten to pack the chain tool they’re sure they have, while someone else may have a stash of zip ties they’d forgotten about.
5) Be orderly about your repair. Lay out tools and components on a coat or rock so nothing goes missing. Work methodically and safely. Don’t injure yourself in the process of fixing the bike.