Reverse shaping is used for fronts. The first shoulder is given with decs at the armhole and neck edge; for the other shoulder you may do the decs on the opposite edges. An armhole usually starts on the RS with BO x sts, then at the beg of the next RS row dec 1 st, dec 1 st at neck edge. The other side, you BO at the beg of the WS row and make your neck dec at the end of that WS row. The middle sts will be bound off somewhere before you begin to dec for the neck edge.