St John Ambulance has a page containing advice on treating nosebleeds .
Specific points relating to stopping a nosebleed quickly are: Advise them not to speak, swallow, cough, spit or sniff because this may disturb blood clots that may have formed in the nose.
Ask the casualty to breathe through their mouth (this will also have a calming effect) and to pinch the soft part of the nose.
Tell the casualty to keep pinching their nose (for 10 minutes).
Importantly, their advice is not to tip the head backwards :
Do not let the head tip back; blood may run down the throat inducing vomiting.
Instead, the casualty should "tilt their head forwards to allow the blood to drain from the nostrils.
" "Shut up, stay still, stop sniffling, pinch your nose, and tilt your head forward" might not be the most reassuring advice, but it is probably the most effective way to stop a nosebleed quickly.
martialarts.stackexchange.com/users/17/Nick
After getting my nose broken I had perpetual nose bleeds for about a month, I usually had about one each day that would just spring up randomly.
My brother was training to be a paramedic at the time, so he knew how to deal with it and taught me.
Presumably as it was from his paramedic training, it's well researched.
1
: Look down, not up.
You don't want the blood draining into your throat and your stomach.
It's unpleasant long term, since you won't digest it very well, and there's a tendency to throw up if you get too much blood.
2
: Pinch the soft part of your nose for 10 minutes.
Don't let go to check if you've stopped bleeding, that's probably the most common mistake I see.
If it's not really bad you might be able to get it done in just 5 minutes, but if after doing it for 5 minutes once you find it's still bleeding, just stick with 10.
And from the ENT specialist who did surgery to stop the bleeding from starting again.
Presumably his advice is well researched as well.
3
: Put a generous dose of Vaseline inside your nostril to keep too big of a scab from building up.
If the scab breaks off, you get the nose bleed all over again, so you want it small enough that a light hit to your nose doesn't break it off or that sneezing doesn't blow it out starting a new bleed.
martialarts.stackexchange.com/users/565/Robin Ashe
As an EMT I would have you sit down and lean forward where your elbows were supported on your knees.
With a clean rag or paper towel try to compress your nostrils, or pinch them closed if not to painful.
This will prevent blood form going back into your throat and allow it to pool in the nostrils and form a clot.
Depending how bad it is it should stop quickly.
Blood is a very powerful gastral irritant, try avoid swallowing any.
martialarts.stackexchange.com/users/51/Swift
I used to wrestle and I get nose bleeds very easily.
In wrestling, you only have a couple minutes to stop a nosebleed before you forfeit the match.
As weird as it sounds, we would use a small tampon.
Just stick it up there and tilt your head forward.
It'll be stopped very quickly.
martialarts.stackexchange.com/users/66/Beaker
Keep your hands up! :)
It's easy to get a nose bleed, especially if you've had a few of them.
There are many ideas — I haven't tested any of them myself, but I've heard some of them debunked.
The most common one, is to tilt your head backwards — this won't stop the bleeding though, but you may keep it from soiling your clothes for a while.
Be careful about lying down, as the blood will only be redirected the wrong way, and that might harm you.
What I would do, is to tilt the head forwards while pressing the nose, so that the bleeding is stopped.
After a few minutes, the blood should clot naturally.
If the nose bleed doesn't stop, seek immediate medical advice.
martialarts.stackexchange.com/users/30/Nix
The most common advice that I usually hear is to just pinch your nose, which reduces the blood flow.
If the bleeding is a bit heavier, then using a moist teabag (black tea) is known to help as well due to the tannins in the tea.
Additionally, the bag itself acts as a poultice to help absorb the excess blood.
martialarts.stackexchange.com/users/46/anonymous
To stop a nosebleed first, hold your nose with a soft cloth, a tissue, or, a clean cotton wool.
This will reduce the mess of flowing blood and will result in lessening your irritation with the nosebleed, when its over.
Second, while holding down your nose with a soft cloth through one hand, lean forward as much as you can, and pinch your nostrils with another hand for 10 minutes, at this moment you can breathe from your mouth.
Try to wait for maximum of 10 minutes.
It seems difficult, right?
But, in order to stop the nosebleed quickly, its worth to hold on for such a long time.
martialarts.stackexchange.com/users/955/Himanshu Sharma
I have found an instant way to stop nose bleeds.
I mix powder collagen (from GNC, Vitamin Shoppe or any health food store with a few drops of water to form a paste and put it in your nose and dip a twisted up paper towel pack in the collagen paste and put into the nostril.
Hold for a few minutes.
But it Stops instantly.
Amazing.
martialarts.stackexchange.com/users/6200/Judy Saso
Use NoBleed twice a day for 1 month and then once a day for one month before wrestling season
and then once a week after that during wrestling season to PREVENT the nosebleeds from occurring.
It works.
Also can be used by non-wrestlers who are affected by chronic recurrent nosebleeds...
martialarts.stackexchange.com/users/6468/Bruce Hudkins
I tend to suffer a number of these in training.   Various people have various ideas on ways to quickly stop the bleed.  Is there a well researched way to quickly stop a nose bleed?
What's the best way to stop a nose bleed quickly?
martialarts.stackexchange.com
<injury><health><safety>
martialarts.stackexchange.com/questions/28
martialarts.stackexchange.com/users/8/Keith Nicholas
Specific points relating to stopping a nosebleed  quickly  are: Advise them not to speak, swallow, cough, spit or sniff because this may disturb blood clots that may have formed in the nose.  Ask the casualty to breathe through their mouth (this will also have a calming effect) and to pinch the soft part of the nose.  Tell the casualty to keep pinching their nose(for 10 minutes). Do not let the head tip back; blood may run down the throat inducing vomiting. "Shut up, stay still, stop sniffling, pinch your nose, and tilt your head forward" might not be the most reassuring advice, but it is probably the most effective way to stop a nosebleed quickly. When pinching the soft part of your nose for 10 minutes, don't let go to check if you've stopped bleeding - that's probably the most common mistake.  An EMT would have you sit down and lean forward where your elbows were supported on your knees. St Johns ambulance has a well researched way to stop nosebleeds that can be applied to training with other recommendations including  the avoidance of  coughing, spitting and sniffing, as well  the use of vaseline in the nose and 'Nobleed'. 
St Johns Ambulance has a researched page document. Other ways include avoiding coughing, spitting and sniffing, looking up, pinching the soft part of the nose, vaseline in the nose and using Nobleed