On your own, you can do whatever you want - it's your own little box.
If there are two of you, you take different corners. Standing diagonally across from each other creates the greatest distance.
When a third person enters, you will unconsciously form a triangle (breaking the analogy that some have made with dots on a dice). And when there is a fourth person it's a square, with someone in every corner. A fifth person is probably going to have to stand in the middle.
Now we are in uncharted territory. New entrants to the lift will need to size up the situation when the doors slide open and then act decisively. Once in, for most people the protocol is simple - look down, or examine your phone.
From the BBC.