Pranayama is generally defined as breath control. The word pranayama is made of two roots: prana
plus ayama. Prana means "life force"'. It is the force which exists in all things.Whether animate or inanimate. Although closely related to the air we breath,it is more subtle. Pranayama utilises breathing to influence the flow of prana in the nadis or energy channels.
Ayama is defined as "'extension or ''expansion'. Thus,the word pranayama means ëxtension or expansion. The tecniques of pranayama provide the method whereby the life force can be activated and regulated in order to go beyond ones normal boundaries or limitations and attain a higher state of
vibratory energy.

When sufficient life energy is produced through proper breathing, the mind grows stronger and sharper. Breath, life force,and mind are interconnected.
Improper breathing creates less life force, which results in poor health and an unsteady mind. By practising deep breathing eexercises one can learn to breath fully and correctly.
After the practice of pranayama,meditation,naturally follows. Practices of yoga (Yoga literally means únion) purify the bodyand the mind for the purpose of developing concentration.
Pranayama is the fourth stage of the - eight - stages practice of Yoga as described by Patanjali(Ashtanga Yoga; ashta=eight):

1. Yama=restraints
2. Nyama=observances
3.Asanas=postures
4.Pranayama= Control of breath
5.Pratyyahara=control of senses
6.Dharana=concentration
7.Dhyana=meditation
8.Samadhi=self-realization

YAMA
AHIMSA: Non-Violence with mind,action,and speech
SATYA:Truthfulness(avoidance of all falsehood, exaggeration and pretense); it is necessary for the unfoldment of our intuitive, discriminating faculties.
ASTEYA:Non-stealing, (Not only physical objects but also qualities that are not rightly ours.)
BRAHMACHARYA: control of sensual desires, allowing one to use that energy for higher purposes. Translated as celibacy; it more properly refers to continence in either celibate or married life.
APARIGRAHA: Non-possessiveness, using the things of the world for their intended purposes, without a feeling that you are owned by them.

NIYAMA
SAUCHA:Purity,Purify the body by pure, healthy foods and by practices of cleansing exercises. Purify the mind by getting rid of nagative thoughts and emotions.
SANTOSHA: Contentment. Outside influences should not disturb your inner tranquility.
TAPAS: "That which generate heat Refers to action actions, disciplines, and aausterities which purify the mind and the body.
SVADHYAYA: study of the scriptures and of the internal states of conciousness.
ISHWARA PRANIDHANA:Literally means:'Surrender to the Ultimate.

Four aspects of pranayama
In the pranayama practices there are four important aspects of breathing which are utilised:

a) Puraka or Inhalation
b)Rechaka or exhalation
c)Anter kumbhaka or breath retention(full lungs)
d) Bahir kumbhaka or breath retention (empty lungs)

Prana and lifestyle
Lifestyle has a profound impact: exercise, work,sleep,intake of food, sexual relations,emotion, thought and imagination all affect the distribution and flow of prana
in the body. Irregularities in lifestyle, dietary indiscretions and stress,deplete and obstruct the pranic flow.
Breathing: Always breath through the nose. (The nose may be cleaned regularly by jalaneti
tecnique). While inhaling, the nostrils should dilate and while exhaling, they should relax back to normal position.
Those who breath in short, quick gasps are likely to have a shorter life span than those who breathe slowly and deeply.
Time: The best time to practise pranayama is during the early morning(when the body is fresh and the mind has very few impressions) or sunset. Try to practice at the same time
and place each day.

Place:Practise in a quiet room, well ventilated or outside. Avoid practising in direct sunlight, except at dawn when the soft rays of the early morning sun are benefical.
Position: A comfortable, sustainable meditation posture is necessary with the spine, neck and head erected.
Sequence: Pranayama should be performed after asanas and before meditation
Clothes:Loose,comfortable clothing.(waist and chest free)
Bathing: Take a bath before the the practice or at least wash the hands, face and feet. Do not take a bath for atleast half an hour after the practice to allow the body temperature to normalise.
Empty stomach: Wait at least 3 hours after meals before starting pranayama,as food in
the stomach places pressure on the diaphragm and lungs.