Do it before you make your monster in case you get something what requires a special body. Keep your power secret until necessary. Put monsters on the playing field. Floor is good, but table is good too. Everybody roll a die for the round.
Players move in order from lowest die-roll to highest.
Player with lowest initiative moves first. Player may move their monster up to the number of handspans agreed upon. Oh, yeah, compare handspans beforehand to make it more fair - you don't have to use a ruler, just tell some people to stretch and some people to compress. Everybody Moves their Monster. If you do, it takes all your movement.