During yoga nidra there is no need for physical contact between the teacher and the practitioner. The only contact should be psychic and through the sound of the voice.
The teacher’s voice should be calm and clear. The speed of instructions should be varied according to the needs of the situation. The teacher must feel the needs of the student(s). Intuition is required. The instructions should be sufficiently fast that they capture the attention of the practitioner and prevent the mind wandering here and there or brooding on problems; but not so fast that the instructions cannot be understood or carried out. If necessary, there can be frequent repetition of the instructions. When the practitioner reaches deeper states of relaxation then the instructions can be slowed down.
Suggestions and dogmas should be avoided. The instructions should be concerned only with the explanation of the mechanics of yoga nidra and the sequence of practice. The tone of voice should be modulated to suit the circumstances.
For the practitioner, the voice is very important. It is the link that enables you to maintain awareness while exploring the deeper layers of the mind. Without a guiding voice you will surely lapse into sleep (which is, however, perfectly acceptable in cases where the practitioner is very tired and perhaps suffers from insomnia). Do not intellectualize about the instructor’s words. Do not try to remember them. Just follow them spontaneously without too much effort. Flow with the sound of the voice.