One of my favorite exercises to do with musician and non-musician clients is to lie on a foam roller, using the roller as a feedback tool to find asymmetry in the shoulders. Most instrumentalists play an inherently asymmetrical instrument, which means that over time the spine and shoulders may adapt to that instrument, creating a slight rotation, side bend, or anterior shift of the shoulders.
While there are many amazing abdominal and core exercises that can be done on the foam roller, I start with a snow angel movement, letting the backs of the hands and arms be as heavy to the floor as possible. From here, clients can start to feel the movement of the shoulder blades as the arms move and feel a sense of stretch in the front of the chest.
The second piece of the exercise involves keeping the shoulder blades wide apart, slightly protracted, and then continuing with the snow angel movement, which may intensify the sensation in the front of the chest. A third way to increase the challenge is to add a small 1-2 pound hand weight to the movement, letting the hands hover just off of the floor, now challenging the front of the chest to manage a low load in this lengthened position.
There are many other possible variations from here: externally rotating the shoulders more fully, adding more weight, transitioning into arm circles, and more, but I find this to be a perfect foundational reset for clients who may be unaware of their shoulder position and who need to gain a sense of length in the front of the body prior to doing other movements.
