The word Guna is a Sanskrit word that translates as “quality” and it represents the three-fold nature being; tamas, rajas and sattva. According to the ancient Yogi scriptures these three qualities or states combine in various proportions to give rise to the objects in the world, including ourselves. The Gunas go on changing every moment. Only the soul or purusha is beyond the scope of these transformations.
The three Gunas have the following qualities;
Tamas: structure, inertia, stability, darkness
Rajas: movement, activity, expansion/contraction,
Sattva: balance, pureness, harmony, light, purity
The three Gunas are present in all human beings but they are not constant. Sometimes sattva predominates, at other times Rajas or Tamas predominates. The Gunas and human nature can be seen as;
Tamas: procrastination, laziness, dullness, depression, ignorance, lethargy
Rajas: cravings, desire, greed, anger, passion, anxiety, discontentment
Sattva: knowledge, peace, harmony, goodness
The Gunas and food is also good one to examine and it may change your perspective on what you eat.
Tamas: stale, frozen food, artificial additives & preservatives, long shelf life products, re-heated food
Rajas: spicy and hot food like onions, garlic, chilli
Sattva: fresh organic produce, food with low food-miles i.e. straight from garden to table, not overly stimulating, good food combinations i.e. lentils & rice, or corn & beans, food that is easy to digest.
Yoga & auspicious living
Yogic practices awaken sattva but this requires more more than just practicing asana and pranayama. In the Bhagavad Gita the important practices of yoga which develop one into a Yogi are Karma Yoga, Bhakti Yoga and Jnana Yoga.
With continued and consist dedication to the path of yoga the mind becomes less influenced by the Gunas to a point where supreme awareness is achieved which is ultimately freedom from the Gunas.
For most of us the everyday-life awareness of the Gunas gives one a practical starting point for living life auspiciously e.g. shifting behavior from tamas to rajas, or rajas to sattva. It is sattvic behavior which lifts the spiritual aspirant from the mundane and inauspicious living, to auspiciously living their lives.
Bhagavad Gita - https://www.asitis.com/
The Yoga Sutras - Chapter 1:16, Chapter 2:18 & 19, Chapter 4:13 & 14, Chapter 4:33 http://www.swamij.com/yoga-sutras-intro.htm
Taming the Mind - http://www.yogamag.net/archives/1979/emay79/taming.shtml