If you are a 1st Aider on the scene, your personal safety is the Most Important of all. If something happens to you, you can save no lives!
Look around, assess the situation. Is it safe for you to proceed? Where is the shooter? Does the injured still have a knife or firearm in his hand or close to him / her? If you are not familiar with firearms it is time that you become familiar with their safe handling so that you can make safe that firearm before you proceed with 1st Aid.
Using protective equipment like safety glasses (blood splatter into your eyes), medical gloves (keep blood off your hands and possible cuts you might have on your hands) and maybe even a medical face mask (blood splatter into your nose / mouth) is essential to keep you safe.
Next you need to ensure the scene is safe for the victim or injured person. Are they lying in the middle of a street or road. Let someone stop traffic before a car crashes into you and the victim!
Are people still shooting on the scene?? Can you get the victim safely behind cover without disrupting his spine / neck and without putting yourself at risk?
We need to think about these points in different scenarios and about what solutions will be safe and applicable.
Think, Prepare Yourself, and When Sh!t Happens you can Prove Superior!