As someone who has had at least
several thousand blood noses in their life, I can offer a couple of tips from personal experience:
If the bleeding is relatively minor or slow, it is possible to keep it in check by lightly and consistently sniffing, not enough so as to draw blood into your sinuses, but just enough to stop it dripping. The airflow also speeds the clotting, and it involves no use of unsightly bloody tissues.
If you're anywhere near a sink it can also be beneficial to hold the bleeding nostril under cold running water. I've found this is best when the bleeding is out of control (as a result of excessive heat or high blood pressure, two things that invariably result in nasal haemmorhage for me).
For all levels in between, the tissue plug or fingers-as-pegs methods are both adequate. Where you hold your head is pretty much irrelevant, but I don't recommend a position in which the blood can flow into your sinuses, for this is very unpleasant. Don't hold your head back, and I personally wouldn't suggest lying down on your back either.