I agree with Howie70; the only thing I would add is that the DW usually stands near the rear of the trailer on the side I can't see. The rest of the time she stands near the rear of the trailer on the driver's side. It is VERY important to use hand signals and doesn't matter what they are as long as both of you understand what they mean. We use:
Closed fist = Stop
Wave Hand Forward = Abort and make another attempt
Pointing finger left/right = In direction the trailer needs to go
Palms facing each other = Indicates how close trailer is to stop point
Practice is the key and you will know when you are improving when the frustration and yelling stops.