Squeeze at the base of the bone - you can feel where it is - for about 15 minutes. If it doesn't stop, call the doctor. Also, don't blow your nose, because you'll dislodge any clots that have formed.
And don't tip your head back - you'll just be swallowing blood, which will give you the joy of being nauseated as well as having a nosebleed. Instead, lean forward a little.