I generally sketch out a map showing rough positions before kicking off. It gets scrawled upon extensively, and I continuously describe the positioning in each round, e.g. "OK so now the three of you are in a line up against the one velociraptor (V3) whilst over to the left the two others of you have three of the velociraptors on you. Player: "How far to the left are the other two?" Me: "Ermmm 20 feet. Or 25." Player "Can I dash over there and help them out?" Me "You'd have to disengage unless the velociraptor in front of you drops first. Oh, there is some difficult jungle terrain around...but the short way over to the other group is clear for you" etc. etc.