No sewing required, you just need a pair of fabric scissors.
Watch the video tutorial:
Step 1: Cut the neckline
Start off by prepping the neckline.
Decide how you'd like to cut the neck off - Follow the original seam so your cut will be even. Cut 1in wider than the original neckline for a roundneck. Cut 1.5-2in wider than original neckline for a wide, boatneck or off the shoulder neckline. Do not cut more than that because when you stretch the fabric it becomes much larger than you expect.
Step 2: Decide the Shape of your V
Then decide the shape of the "V" that you want. The wider, or deeper the V, the sexier and more revealing the shirt. Place a rule to outline where you'll be cutting.
Step 3: Cut your strips
Step 4: Stretch the strips
Stretch out the fabric to roll edges. Gives it a cleaner look. Hides any imperfections from cutting.
Take each strip that you cut and pull it out so it turns into a thin and even strip.