What are the ways to maintain a healthy, stress-free, and tranquil life, using the conscious, subconscious, and superconscious mind?
This is a very good question, as all three levels should be activated and included.
For the conscious mind: this is your intellect, your rational faculty. Analyze carefully what you need to do and to avoid to maintain a healthy, stress-free, and tranquil life: what foods to eat; what environments to avoid and which one to seek out; which inner attitudes to cultivate; which changes to make in your lifestyle.
For the subconscious mind: Yogananda teaches to infuse it with positive messages, applying affirmations. So get a good book on affirmations (like Yogananda’s Scientific Healing Affirmations, or Swami Kriyananda’s Affirmations For Self-Healing) and regularly send these good messages of health, tranquility, and peace to your subconscious mind. This is highly important as it influences us greatly.
For the superconscious mind: this is the part of the mind which infuses your understanding and solutions from “above”, intuitively (not rationally). The best way is to meditate and get as calm as possible. Then, at the end of meditation, concentrate on the seat of superconsciousness at the spiritual eye between the eyebrows, and ask there: “How can I maintain a healthy, stress-free, and tranquil life?” Then be open to answers coming from within, or also from anywhere, anyone. Somehow the universe, or the Divine, will answer you, if you are open to a higher guidance. You can also ask at the spiritual eye, for example: “Is this correct?”, as you think of some action, or food, or environment. Then try to intuitively feel the answer in your calm heart. Again, it works best after meditation.
All the best to you, may you learn to apply successfully all three levels,