Watch Sun Salute A Tutorial Up Dog Bad Dog
How to practice upward facing dog.
How to modify downward dog with tight hamstrings.
Transitions are an integral part of the Ashtanga practice. The more we practice them, the smoother, more seamless the practice becomes.
This is a good place to start. Sun Salutes can be a complete practice or they can be a warm-up. If you're newer to the practice, start here. This will help you to link your breath and movement and to increase your stamina.