The asana, the posture, you adopt to practice pranayama should be straight. Tristhana - the head, the neck and the chest should be held up and in a straight line. You should keep your mind pure.
There may be pranayama which a few schools call by a particular name and some other schools call the same pranayama by a different name.
Everyone loses flexibility and the body reflexes. This forces them to go for simple practice.
When you practice pranayama, try to practice at a particular hour of the day, especially during the early years of your practice. This is because the body and the mind have peculiar behaviour.