The rule of thumb is to be respectful when a funeral procession crosses your path. If you are driving, pull over to the side of the side until the procession passes. If you are standing, as you ask, then remain where you are. If you are wearing a hat, remove your hat until the procession has passed. Hands should be clasped in front with your head slightly down. Don’t stare at the line of cars or wave at the people in the vehicles.