How do you help a person who is unconscious?

First, call for help, or send two people to get help. Tell them "CALL 911!". Don't use the word "help" -- it just confuses them. Tell them exactly what you want them to do. If you're alone, think about the situation and decide what to do first; call for help or attend the patient. It can be a tough decision.
Next, make sure that you and the victim are in a safe place. You can't help someone in the middle of a busy street. If you have to move them in order to keep the two of you safe, do so, but if you have any reason to suspect a neck injury, try to move them without moving the head or neck out of line. If you don't have to move them in order to stay alive, don't move them yet.
As you approach the victim, and once you're there, nefore touching, try and figure out what happened. Downed electric lines shocked them? If so be SAFE. A piano fell on them? Watch for crush injuries and watch that spine. No idea why they're unconscious? Okay -- that's a start.
Next, check airway, breathing and heartbeat (ABC -- Airway, Breathing, Cardio). If they're breathing and their heart is beating -- good -- most of your work is over. If ANY of these things isn't working, fix it. Airway first, then rescue breathing (if necessary), and CPR (again, if necessary).
Check for severe bleeding. If there is severe bleeding, stop it with direct pressure.
If none of these things apply so far, or you've found and fixed some or all of them, then assess. Will the patient respond to noise? If you know their name, call it -- quietly at first, then loudly -- see if you can get them to respond. If you can, see if they're confused. See if they recall who they are, where they are, and what happened. If they don't or can't answer, go on to the next part.
IF THERE IS DAMAGE TO NECK, HEAD OR SPINE, DON'T MOVE THEM. Unless they stop breathing or their heart stops, leave them be until help arrives. You can cover with a blanket if it's cold, or shade if it's hot.
If there is no apparent risk to the spine, If they're unconscious, try putting them on their left side, face pointing sideways/down, so if they vomit they don't inhale it. If they're conscious, try putting them on their back with legs elevated above the heart.
Maintian body temp -- if it's cold, warm them. If it's warm, shade them.
Do not give water or foods. Do not shake them. Don't offer smelling salts. If they have their own meds and want to use them, let them.
Wait there until someone qualified takes over or the patient wakes up and leaves. If you think the patient needs to be seen by a professional, feel free to talk them into it, but don't touch or try to restrain them.

first, call 911 immideitly!
if they are completey unconscience, the CPR has to kick in.
lay them on there back and sit up next to them
place hands exactly on the sturnum (just below his ribs) and give 30 fairly hard thrusts to that area. do not give THEN THRUSTS ON THERE RIBS-- YOU COULD BRAKE THEM AND THE PERSON WOULD HAVE NO HOPE!!!!!!!
open there mouth and breath in to it twice, each breath shoould take about one second
tilt there head back and listen for breathing, if not, pinch there no9se and breath into it again twice.
repeate all steps untill 911 arrives.
if they wake up, you should still wait for 911, they might want to do some examing just to make sure the victim is ok!

(bold part "improved" by kdiehl)