At what point do you step in and offer help?

I am like one of the previous posters, I do not run up and say here let me help but will help if asked. Here is one of the biggest things I have found with the inexperienced backers. They will get it in their head that the mirrors reverse the image and that they need to go the opposite direction and then they get in a hurry and all heck breaks loose and they forget everything. I can usually offer one small tidbit of information that I used on students when I was an over the road driver instructor. I will talk to them enough to settle them down a little and then explain to them to think of the steering wheel as the trailer as they sit in the seat. The top of the wheel represents the front and the bottom the back. Then to sit straight in their seat and trust the mirrors and to place their hands on the wheel in accordance to which end of the trailer they want move and to move it towards whichever mirror they want that end to go to and travel slow and follow then catch up. With that advice and just a little coaching I have been able to walk them right into where they were headed. Once they are in and setup we can discuss the particulars over a glass of iced tea. Like the shorter the trailer the shorter the reaction time to catch up with TV and so forth.