If the discomfort is acute and has developed recently, you will probably prefer to work on the symptoms first.
The simplest thing for helping neck and shoulder tension is to hold your shoulders, SEL 11 (SH 2, p. 32). Instead of holding both SELs 11, you can also combine SEL 11 with placing your thumb over the ring finger (Mudra No 6, T1, p. 47) You can use the Supervisor Quickie and the Bladder Flow to clear up all the back – from head to toe.
Each of the finger flows goes through the area of SEL 11 and then flows along the neck into the face/head area. Also, the anchor step for each Finger Flow includes holding SEL 11. For the Large Intestine – hold SEL 11 and Index Finger (T2, p. 13), for the Small Intestine – SELs 11 and 13 (T2, p. 21), and for Umbilicus Self Help – SELs 11 and 12 (T2, p. 31).
Once you clear up the symptoms, for them to not reoccur, you need to look into the causes for that disharmony. You can still do the same flows before, but not because of their energetic pathways but rather because of their relationships.
Tension in the neck and shoulders seems to be related to stubbornness. So, any flow that helps with letting go of crystalized attitudes and habits can help. Liver Function Energy is considered a good lubricant of the body and hence is a frequently recommended flow for stiff neck and shoulders. Especially when the condition has become chronic.
You can also play with the Safety Energy Locks keywords. SEL 16 is Transformation and helps with getting un-stuck and transforming old patterns into new. SEL 8 is about the magic and the miracles that we are entitled to. Number 8 is also the number governing 3rd Depth within which Liver Function Circulates. Holding them together (SEL 16 with low SEL 8) is actually the hold for Special Body Function 2 which helps with stiffness projects.