To supervise a learner you must be 21 or over, have held a full licence for the category of vehicle for at least three years, and the car must be insured for the learner. Display L plates (D in Wales). Motorways are only allowed with an approved instructor in a dual-controlled car, not with a parent.
Private practice helps most when it repeats what the instructor is teaching, not when it introduces a different method. Ask the instructor what to practise this week. Stay off the test routes the night before a test — tired and tense is a bad combination.