"What sort of things might I fail on?"
Among the many reasons for failure, the most common are:
too long a briefing or one which is muddled or repetitive;
expecting too high a standard from the 'pupil' in the beginner or parttrained stage;
not instructing at a level appropriate to your pupils needs (over or under instructing)
inability to recommence instruction at a different point or to go back and explain again;
failure to detect faults;
treating a 'pupil' as a novice in the trained stage;
inability to adjust the content level of the lesson to match the 'pupils' knowledge;
demoralizing the 'pupil', eg, "The Examiner will fail you if you do that on a test".