In most of my sweaters you will only have two short seams on each shoulder; the top, bound-off edge of the front to the sloped back shoulder and the top, bound-off edge of the sleeve to the side of the front. Since there are only two little seams it’s worthwhile getting them right. They are both invisible vertical to horizontal seams.
In preparation for these seams remember that anytime a BO edge is going to be seamed to something, you should bind off in Stockinette stitch, not in pattern. If you are working in pattern don’t worry that the St st BO row will show, it will disappear in the seam. But doing this will make working the seam much easier and why not make things easier, knitting is supposed to be enjoyable!
I like the seaming illustrations at Vogue Knitting. Scroll down until you find the directions for the Invisible Vertical to Horizontal seam.