I do different guided relaxations. When I do Yoga Nidra, I follow Swami Satyananda Saraswati's method with a long and calming preparation time. The practice itself is a systematic physical, mental, emotional and energetical relaxation through the rotation of awareness in the body, observation of the energy and archetypal mental visualizations.
From time to time I give Yoga Nidra workshops. Then the practice is done on several successive days and allows students to relax without preparation and to go to deeper realms of consciousness. Sometimes this practice is part of my retreat program and then it's done daily. It's like any practice, first you become familiar with the structure and how it affects you and then you can start to explore more.
When I do intuitive guided relaxations, I either stay in silence, I talk, chant or sing.
Usually people can't relax suddenly to a completely new level of non-control where the fears may come up and thus there's no risk to go too far. Nevertheless I prefer doing yoga nidra sessions on successive days only with regular asana practitioners who have worked with their bodies and energies for a longer period of time. This is due to the fact that some people are able to let go of control, but can't handle the consequences. When the relaxation deepens, the subconscious mind begins to express itself.
It's essential to be able to relax to go further in any kind of yoga practice. A tense mind makes us confused and anxious which means we are not present in this moment, not receptive. The relaxation as a part of a yoga workshop is meant to relax more deeply the mind, the emotions (the energy field) and the body to be fully present and to go then towards the new with an open mind.
A deep relaxation means to let go of our ego, our opinions and mental patterns. This is often scary. Gradually we get used to a state where our thoughts don't give us any support and this kind of space becomes our natural state. We become more aware of the reality instead of our thoughts. A sharp concentration (Dharana) and meditation (Dhyana) can happen only with a pure, relaxed mind.