Dhyana is actually a mental activity and has little to do with bodily postures, but having said that a comfortable posture might be helpful in quieting the mind.
The Swetaswatara Upanishad says that the head, neck and shoulders should be held straight and steady while meditating. Then one should think of AUM. AUM is the Shabda (Nada) Brahman, the primordial sound. (Think of A as creation, U as the steady state and M as destruction). Just imagine that all the three is happening when you mentally pronounce the word. It would move us away from hindering thoughts and would help to still the mind.
I might write something on the worship of AUM sometime later. But really it’s not needed. It’s only a boat to steady the mind for further activity.
As you stay like that in your place of meditation you will notice the thinning of breath. At that moment you need to close your mouth and begin Pranayama. The Rishi prescribes Rechaka-Puraka-Kumbaka’s (You might want to look up the article on Pranayama to learn what it is). But to me such strenuous practices are not all that necessary. Just steadying the breath would do.
Upanishad says that a flat clean surface with no disturbing sounds or no captivating/awkward sights is preferable to every other kind of sites. Air currents should not also trouble us while we sit thus. Caves are suggested for this purpose. A room is as good as anything else as far as I am concerned, if it’s uncluttered and clean.
If you experience the presence of fog, smoke, sun, gaseous phenomena, fire, star, lightning, crystals and moon in the beginning it would lead you towards the final truth. You can meditate with your eyes open and see all these phenomena in the visible form.
I can assure you of that. These are not mere words; I have been through the experience.
According to Indian cosmology there are five states of matter in our environment. They call it elements. Prithvi (Solids), Jal (Liquid), Agni (energy), Vayu (Gaseous) and Akasha (Space). As you meditate your mind would start to understand how these elements form and evolve into each other. This would give you the Yogic body (that is you would know what the body is really made up of) and thus would eliminate old age death and diseases.
A word of caution: Though this is possible, if you concentrate on these aspects it would lead you astray from the search of truth. These are spectacles by the way side and we should not and stop our journey for them.
The first signs of Yogic state are lightness of body, strength in you, personal beauty, attractive voice, presence of good scents, aversion to worldly things, and diminished quantity of excretions.
All this is true too.
This yogi sheds his vestures and starts to realize his real nature, that is, his oneness with everything. This Deva (Spirit) is nothing but the whole world. He pervades all directions and is the first born in the universe. He is the one in the womb and the one outside and is the one yet to be born. He resides in the hearts of all as the inner spirit. He faces all points in the universe simultaneously.
The second chapter of the Upanishad concludes enjoining us to pray to this god who resides in fire, water, plants and trees and has entered everywhere in the universe.
It technically becomes a prayer to our own true self.