To most, it is common knowledge to lay your head back when your nose starts to bleed. However, you tend to swallow your blood when you lean your head back, which, in return, can form blood clots.

So when your nose starts to bleed, lean forward and just let your nose bleed. If it's really bad pinch the bridge of your nose. But I warn you, once you pinch your nose there is no letting go until the blood has stopped.