If you go up a one way street then you can continue on this road until you reach the next block. It is likely that the road that goes parallel to this road goes in the opposite direction. This would be the easiest way to turn around. If you have gone the wrong way down a one way street then your best option is to pull over to the side of the road and wait for all of the traffic to clear. You can then do a U-turn or a 3 point turn when the road is clear to go in the right direction.