Looking over your left shoulder into the rear passenger door window, reverse back until the rear corner of the target vehicle (the car you're parking behind) appears and then turn one rotation of the wheel left (360º, NOT full lock). Check all around the car, especially over your right shoulder as the front swings out and the back starts to arc towards the kerb. Keep moving slowly until the same back corner of the target vehicle is in the middle of the front passenger window, then turn one rotation to the right (effectively straightening the wheels). Soon after, still looking in the front passenger window, line up the middle of the target vehicle (badge, wiper, boot lock or whatever is there) to the front edge of the front passenger window and turn one full rotation to the right, so swinging the front now towards the kerb as the back arcs towards being parallel with the kerb. If at this point you feel like you might hit the kerb, fully turn to full right lock to try and avoid this. When the car feels straight, turn to the left until the wheel is straight to finish. If you are wide, use a shunt manoeuvre to tidy up (drive forwards slowly turning left/right/left, then reverse back again turning left/right/left).