please excuse the amateurishness of my paint skills, i really do suck at it.
it represents what golfhobo explained. the red line is the line you follow to set yourself up. it's a form of a question mark. by doing this it sets the trailer to automatically go into the hole, and allows you to be jacked to where you can see it.
when you do this, start by following a parallel line to the building, staying somewhat close to the fronts of the other trailers if you need the room on the opposite side to swing the cab around. if not, then i usually stay @ 3' away.
if it helps, when you get your dock, stop and survey the dock. if there are no lines, imagine a line out from the right side dock bumper and lay down a glove at the front of where your trailer will end up. this will give you something to guide off of. then slowly start to aim for the glove with your tires. get out and check as much as you need too.
hth
edit do the opposite to set yourself up to blind side.