Wherever possible I always ask the owner or pilot where to grab the aircraft. Especially with the imaginative designs of the home-builds with which I am usually surrounded, the only way to know for sure is to consult the flight manual, which the pilot is supposed to know (especially if he built it himself.
Otherwise you have to go by the basic principles and common sense - like avoiding wobbly parts, skinny bits and propellor tips.
If a member of an exclusive club which I will not name here (I'm sure present company would not stoop to this, and I thought it had died out, but I've seen it), you don't push or pull it at all: you simply dress in white, flutter your eyelashes, click your fingers and get someone else to do it for you, with a casual warning to avoid touching the tail rotor!