I’m not saying you need to be ready to perform open heart surgery or an emergency tracheotomy as a veterinarian. I am saying that you need should have a basic grasp of how to help when everything goes to shit.
Obviously, calling 911 should be your first move. HERE is a list of 911 alternatives for different countries. I’m not saying memorize them, but at least know that 911 
in Australia is just the first three digits to the number for Domino’s.
I used to work for a volunteer ambulance company. It was interesting, yeah, but the point is this- there is an order of response from emergency units, especially in big cities. Police first, then fire, and ambulance last. We’d always get there and the firefighters would already have the old bag with trouble breathing on the stretcher on the way out the door. It was simply a safety precaution, but there is an important lesson to take from this, which is that 911 dispatchers don’t wait to find out the emergency before deciding on a type of response. So, when you call 911, the FIRST thing you should do is say your location. The instant you say your location, they can get the ball rolling on getting you help. You can fill them in on the rest after.
Second, get a CPR certification and learn some basic first aid. My college roommate is now, terrifyingly considering what I know about him, a doctor, and two of his favorite things to tell me on this subject are 1) how infrequently CPR is, and 2) how little EMTs can actually do for most injuries. But it doesn’t matter. CPR is better than standing there wishing you knew CPR, and for the 1 time out of 50 times that it was going to work, you watching with your thumb up your ass will turn into a lifelong regret and a dead human.
On basic first aid, two words- direct pressure.
On snake bites- don’t suck out the poison.
If you’re still reading this for medical advice- take a long look at your priorities.
In boy scouts, we learned how to throw rope for our emergency preparedness merit badge. I don’t think that’s a bad thing to know how to do.
Think, right now, in your head, what skills you are bringing to the scene in the event of an emergency. Do they meet your own personal standards? Do you 
think you would be more of a help or a hindrance? Are they unique, or do most humans have them? (Even George Costanza could life 100 pounds straight up over his head) If they are not at the level you want them to be, take steps to improve them. I know a NYC firefighter, who is ALREADY A FIREFIGHTER, who is taking nursing classes just to be better at his job. So yea, it’s a safe bet to say that for you, you lazy schlub, you’re not as good as you could be.
The Step- Be ready, but more importantly, ABLE, to help.
Have I Done It- It’s a work in progress.
The 10,000 Steps to Becoming a Man. 