1. Start by putting the shoulder seams together and laying the shirt flat
Notice that the sleeves will be touching.
2.Smooth out the shirt so you get a clean cut
In photo 5 the top left of the shirt will be my front, the top right will be the back of my shirt
It doesnt matter which one you choose since they are the same.
3. Cut a scoop out of the top left.
The closer you cut to the shoulder seam the wider the neck will be.
For example: if you cut close to the shoulder seam you can get an "over the shoulder look", but if you cut a few inches away from the shoulder seam your neckline will not be as wide and will be more like a t-shirt.
I would start by going 2-3" away from the shoulder seam, then cut 2-3 inches down and over. If you want more scoop you can always come back and cut more off.
4. Do the same to the top right side, except you wont cut as far down this time.
You dont want as big of scoop cut out like you cut on the front of the shirt.
Cut 1-2" down and over until you hit the end of the shirt