Sam from Regina has a great tip for managing to paint both sides of a door while working alone.
He puts two long screws or lag bolts into the top of the door and one into the bottom of the door. Then he positions his saw horses so that the door is suspended by these three screws. When he wants to paint the other side, he simply grabs the two lag bolts and flips the door over, pivoting on the one screw on the other end.