Pressure and time
It depends on where the bleed is coming from; the front vessels or the back.
Tilt the head forward to avoid swallowing blood, put steady pinching pressure on the bridge of the nose just below the bony ridge. Heavy bleeds that do not stop may need to be treated by a doctor with cautery or nasal packings. http://www.cfpc.ca/uploadedimages/resources/resource_items/patients/nose.jpg.