|Marcie Tilton describes a technique to curve the hem line on long sleeves: add a piece of scrap tissue to the hem of the sleeve pattern. Mark the hem into even thirds. At the back third mark 1/2" outside the cutting line; at the front mark 1/2" inside the cutting line. Using a french curve, connect the marks. The sleeve hem at the back of the arm is longer than the front of the arm.
p.48 Easy Guide to Sewing Tops and T-shirts, Skirts, and Pants