First, it depends on where we have hurt. If we got hurt on our nose and the blood is coming out then we have to keep our head up or just press the nose after some time when the blood stops wash your face or if the blood is not stopping then go to your school's water cooler and then put cool water on your head and sit somewhere then immediately go to sickroom. i hope this helped you because i was also suffered with the same problem in my school.   
                                                    thank you.