Place people using the definite clues first (ends, middle, opposite seats), then the relative ones. In a circle facing the centre, a person's left is the clockwise direction.
1Directions
Row facing north: left and right are as you see them
Row facing south: their left is your right
Circle facing the centre: left = clockwise, right = anticlockwise
In a circle of 2n seats, opposite seats are n places apart