i would suggest having a look at your cervicothoracic junction C4 to T4 but mainly c7/T1 is porboably really stiff and hypo to start off with. perform a few self mobilisations with movemement with your fingers anchored about he spinous processess while you lift up the oppisite arm into flexion or abduction or with cervical rotation to release these joints. pulloverswould be a great exercise to looses the area also. another favourite is to wrap your hands around your neck attempt to straighten, either standing, on a gymnastic ball or against a wall, this is a tuff exericse so exercise caution while performing it. after releasing the stiff cervicothoracic joints have a look at whats happening at the shoulder joint and scapula with a few simple exercises. look at the joint glide while performing a bicep curl; is the glenohumeral joint moving excessively and in what direction, what is happening at the shoulder blade; when you peform a front raise does the shoulder blade lift or does the shoulder blade lock up with very little movement. check out upper crossed syndrome for more details. the final point i would like to make is; think of the shoulder as bones suspended in a myofascial web forget about the classis anatomy description of muscle attachments ,now remember this: muscles tdo not attach to bone it only ataches to periosteum. periosteum is encapsulated about the bone as a part of the myofascial web and continues on with muscles about the the opposite side forming a myofascial plane. see the work from Thomas myers for further detail, the bones are suspended and maintained in that position through tension of the myofascial cables about the shoulder girdle now identify the imbalance and release.