This has been asked frequently lately so you may want to scroll down for additional responses.
Once you have a sep skein attached to each shoulder, do BOs at the neck edge each time you arrive at the neck. IOW, RS facing, do whatever BOs are req'd at the starting edge. Work across that shoulder. Drop that skein and pick up for left shoulder. Work the 3 BOs for that neck, work across. Turn. (WS) Work req'd BOs for that armhole, work across. Drop skein. Pick up skein for other shoulder and do 3 BOs at neck, work across. Repeat the process again but doing 2 BOs at the neck. (You've done 3 BOs once, 2 BOs once...one time each side.)
BOs always done at start of work, sometimes on RS, sometimes on WS.
Keeping to the knitting basics