How do I position the ladder correctly on the vehicle door before securing it?

You should measure 10mm from the right-hand edge of the door and mark this position with masking tape. Then hook the ladder assembly over the door, lining up the right-hand side with the mark you made. Before doing this, place the Rubber U-Channel (Item 10, 76mm long) over the door edge where the Top Step Plate will be secured. (Page 5)