It is largely practice. For hospital based emergencies we practice common scenarios so that you're not needing to think about the basics during an emergency. So for example learning how to use a crash trolley, how to do basic and advanced life support etc. Different areas will also have scenarios relevant to them - radiology may have have anaphylaxis drills to ensure contrast reactions are dealt with.

But practicing being in any emergency in general helps. You learn how to step back emotionally in any emergency and think. The lack of familiarity and panic is a natural feeling when you don't know what to do but learning how to deal with potential expected scenarios makes you better at dealing with unexpected scenarios in general.

A good thing for most people to do even if not medical is go on a basic life support course. It's a useful life skill but also opens the door to "how to think in an emergency". Do it every year to keep fresh.

Other thing to learn is situational awareness - that is keeping your brain switched on when you enter new or familiar areas. It's a skill that can be learned and translates well into emergencies. For example, when you go to a new place actively think "where are the fire exits?", "what are my escape routes?", "who is here now?", "are there any threats here?". These are things that can seem odd when you first do them but if you do them everywhere you go it becomes second nature and you start doing it subconsciously.

You'll find people who work in hospitals, ambulances, fire brigade, police, the army and more are either directly or indirectly trained to do this. Admittedly not everyone in those areas actually learn it in the same way and some may learn "by accident" or as a side effect of other skills learnt.

Like for example, a nurse may not be taught formally "learn the escape routes everywhere you go" but they will be taught "listen to that alarm, if you hear it you need to do this" and "this is the fire evacuation plan for this floor" or "keep an eye on bed 3, their oxygen sats have been low today" and it can sort of seep in to how you perceive everything. If you're in a noisy, busy and safety focused environment all the time you learn how to adapt and perceive what is going on around you even if you're not consciously aware of that skill or what you're doing.

I think most people can learn these skills. Like anything it takes practice.