Staystitch* at 5mm(1/8") along long diagonal edge of both Front Bodice pieces. Staystich top neckline of Back Bodice. Optional: If your fabric is lightweight and very stretchy, you may wish to also staystitch along bottom edge of front and back pieces.
*(Staystitch to stop your garment stretching out of shape. Use a short stitch length (say 2.0) and a straight stitch (ie not a zigzag). Don't stretch the fabric as you sew and stay inside the seam allowance so the staystitching can't be seen after you sew your garment together.)