I like to work on the sleeves and body separately, just to reduce the bulk of the work. With the body done, it is time to put on the sleeves. First, I put the coat body on a model and marked where the shoulder loops should go. They should run across the top of the shoulder, with the point just touching the collar seam, and the end stitched into the shoulder seam. I matched the notches on the body with the seams on the sleeves and pinned it together. With a mixture of luck and experience, all the work I did re-shaping the sleeve head and armscye evened out, and the sleeve fit neatly into the armscye with a minimum of easing. I always stitch my shoulder seams twice, for strength. Once it is stitched, clip the seam allowance and press the seam open. The tailor's ham is a big help here.