Open shoulders hold the key to good arm balances, twists and backbends. Healthy movement in your shoulders can also help relieve neck pain. Shoulder alignment is established from the very first breath and movement of the yoga practice in the Sun Salutations. Instead of waiting until you're working on an advanced posture, practice healthy shoulder alignment right at the start of your practice to set yourself up for success throughout all the postures.
As you inhale, let the anchors of your shoulder blades drop down to the bottom of the pelvic floor to allow the arms to raise. Keep your collar bone spacious and broad while firming your deltoids and latissimus dorsi. Be conscious about not over arching the spine or splaying the ribs outward. Let the energy rise upwards, out through your fingertips.
Once your arms are straight, look up to your thumbs and squeeze your elbows towards each other to fully straight the arms. Keep drawing the shoulder blades down the back and towards the pelvic floor. Feel the movement in your shoulder joint. Notice where you want to compensate for lack of flexibility and be extra conscious there.
As you exhale, release the anchor of the shoulder blade to make space for the arm to float back down. Be sure that throughout this whole movement there is ample space between your deltoids and your ears. If your shoulder girdle starts to creep up towards your face, draw the anchors of the shoulder blades deeper down into the pelvic floor. After you feel comfortable with this movement, repeat the same motion from standing. Over time, the healthy rotation of your shoulders will be connected to the deep strength of your core.