Yoga helps us in getting healthy & elegant. Whereas Ashtangayog is process of evolving own. It helps in developing sensitivity in our relationships with the outside world. Ashtangayog eliminates individuality and possessiveness, instead creates a sense of oneness with the whole universe.
The control of Vritis is important in Ashtangayoga. There are eight steps of Ashtangayog-Kriya for achiving Yog-Sidhi. 1st is Yama, 2nd is Niyama, 3rd is Asana, 4th is Pranayam, 5th is Pratyahara, 6th is Dharana, 7th is Dhyan & 8th is Samadhi.
Yama - Yama are truth, non-violence, non-stealing, restraining adultery (Aprigrah and Bramhacharya).
Niyama - The trend in retirement from materialism (Vishyabhog) to asceticism.
Aasana - Posture of the body, in general required to remain stable in one position.
Pranayam - Breathing technique used to control breath that helps in improving bio-energy (Prana) in body.
Pratyahara - Withdrawal of the senses is Pratyahara. This involves withdrawal from senses or sensory organs that creates emotions & hinders concentration of the mind. Practice of Pratyahara is important to restore calmness in ones life.
Dharana - Dharana (holding), may call as concentration or single focus. Pratyahara helps withdrawing the senses from external phenomena and Dharana improves mental strength by refining it to ekagrata or ekagra chitta, that is single pointed concentration or focus. It is the initial step of deep concentrative meditation, where the object being focused upon is held in the mind without consciousness wavering from it.
Dhyan - Dhyan (Meditation) is not conscious act of concentration as in Dharan. Instead, in Dhyan person becomes one with the object of meditation and able to maintain this oneness.
Samadhi - Samadhi is a higher level of meditation or Dhyan. It is a non-dualistic state. Samadhi leads conscious to subconscious meditation.