Arm position - Downward facing dog
The placement of the arms during downward facing dog can be a little bit confusing for new practitioners and as well as an experienced one.
It can vary a little bit depending on which yoga tradition your practice is based, but this is the way I find works for most students.
What I show in the video below is me on all fours first internally rotating the arms, then working on externally rotating them. As I go into the downward facing dog, I'm working with the external rotation of the upper arms. Then I internally rotate them for you to see the difference. Notice how my shoulder blades squeeze in together around the straps of my top (internal rotation). Then notice how I externally rotate again, creating space through my shoulder blades, sending my biceps forwards, triceps back.
This movement will follow you throughout your class, especially through your vinyasa. The arms will continue to externally rotate as you move into plank, chaturanga, upward facing dog and back into downward facing dog.
Experiment with it and notice the difference it creates, especially around your neck and shoulders.