The breathing is really the key to everything. For me, the pose or asana has to be done in conjunction with the "Ujjayi Breath", which is a deep continuous in and out breathing through your nose that is accompanied by the ocean sound of your breathing. Each movement has either an inward or outward breath or is held for a certain number of counted breaths (for me five deep and slow breaths). Like a surfer who rides the waves of a real ocean, your inner surf carries you from movement to movement. Your breath directs each movement. Once you get the flow of the breath and the movement together, it is like magic.
For example, the Sun Salutation (A) starts up with a breath, touches ground with an exhale, flatten back with a breath, Chaturanga with an exhale , upward dog with an inhale, downward dog with an exhale, hold 5 breaths, up to flat back with an inhale, touch ground with an exhale and then up to prayer position with an inhale. Each pose has its associated breath and with the Ujjayi breathing (and doing this five times during a normal Ashtanga primary series), you get into a combination of breath and movement that is really great.
Sometimes I think to myself that we are happy going to Yoga class and happy right after it but somewhere in the middle, we want it to end. With the flow that I practice at home, I don't have that feeling very much. It is probably because the focus on the practice at that time is on me, with my pace and it is my flowing. There are no stops for instruction and water breaks. It is movement and breathing for an hour or so.