Answer: do not put any weight on your fractured (injured leg). Sit down or lay back if you can. Prop your leg on a cushy object. Maybe try a backpack if you have one?
Explanation: while 911 is on their way it is important to prepare the patient or whatever to asses the damage done and not do anything to make it worse. The ambulance people will take care of the fixing your broken leg part. But at least your making their job easy.