It’s often useful if a learner is able to sing the tune they’re trying to learn by ear. As a first step, introduce the melody in a key which fits the student’s singing or humming range, probably quite low down in their range so that they don’t have to sing loudly. This key may not be the one in which the learner will finally play the piece but this can be introduced later. The teacher might play or sing the first few notes then allow the student to experiment until they find the tune.
With learners who lack confidence and need early success, the teacher may wish to provide the starting note. This can be faded out as confidence is gained.
Happy Learning!