Step 1: Step 1 - Choose your garment
Step 2: Step 2 - Mark the back
Then, align the 1 inch mark of your ruler/tape with the top center point line and make a small reference mark 1 inch from both sides of the center.
Step 3: Step 3 - Prepare and cut out the back shape
Then, all along the inside of the shape you marked, mark a 1/2 inch seam allowance (shown in blue) and then cut out the shape along the seam allowance line.
Step 4: Step 4 - Pin and sew the back shape
Then sew all along the shape.