Top of the list........
A GPS can only give tracking advice when it is moving.
New users have an irresistable urge to stop and look at the GPS - like they would a compass.
When following a track using the "Arrow" technique there my be temporary offsets.
Normal small errors in positioning become important when you are close to a stored point.
When following a closed-loop route, do remember to walk 50m or so along the route before commencing navigation. Otherwise you may be told "You have arrived at your destination".