Stop the activity, check the red flags (deformity, numbness, uncontrolled bleeding, inability to bear weight - those mean get seen now), then start the basics: protect it, ice it 15-20 minutes at a time, compress with an elastic bandage, elevate above heart level.
What to skip in the first hour: heat, alcohol, and "walking it off" all make swelling worse. And the red-flag check comes before the ice: a deformed limb, a numb or blue extremity, a deep wound, or a head or neck injury is not an ice-pack situation - it is urgent care, the ER, or 911.
What to do
Common questions
What should I do in the first hour after an injury?
In order. First, stop. Whatever you were doing when it happened, continuing is the single most reliable way to make an injury worse. Second, run the red-flag check, because it decides everything else: is the limb deformed or bent wrong? Is there a deep or gaping wound, visible bone, or bleeding that pressure does not stop? Is the area below the injury numb, cold, blue, or pale? Can you bear weight or use the limb at all? Did you hit your head, and are you confused, vomiting, or unusually drowsy? Any yes means skip the rest of this list and get seen - urgent care or ER, and 911 for head or neck injuries or anything with chest pain or trouble breathing. Third, if the red flags are clear, start home care: protect the area, ice 15 to 20 minutes at a time (cloth between ice and skin), a snug but not tight elastic bandage, and elevation above heart level. Fourth, skip the old advice: no heat in the first day or two, no alcohol, and do not "walk it off." Finally, set a checkpoint: a straightforward sprain should be clearly improving in 2 to 3 days. If you want a read on your specific injury right now, a free text consult can tell you in minutes which of these paths you are on.