Once the neck gussets are in place, the next task is attaching the collar. In principle this is done in exactly the same manner as attaching the cuffs. There are some slight differences, though.
Instead of running an unbroken pair of gathering threads around the neck opening, I start in the centre back and run two pairs, one to either side. It makes it easier to distribute the gathers evenly. Once you've run the threads through, draw up the gathers until the neckline is the same length as the collar and tie the threads in place.
Mark the collar in the centre and then in quarters.
The quarter points are located in the centre of the neck gussets, so line the collar up and pin the inside into place. If you've embroidered the collar, this is the plain side.
Whipstitch the long bottom edge in place.
Pin the outside of the collar into position and whipstitch it into place, starting along one of the short sides.
You've now finished the neck opening and collar of the shirt and consequently all the really fiddly bits. The rest of the shirt is just plain sewing.