Cut the sleeves off of your shirt, going inside of the stitching

Make thick lines on the shirt. There should be 3 on the front, and 2 on the side, each about 3/4 of an inch thick.

Mark a deep scoop neckline and cut it out. Cut through both sides of the shirt.
The straps of the shirt should be about an inch thick, but you can make them thicker if you wish.

Pick a spot in between two lines and fold the shirt. Make slits along the fold, making sure that you don't cut through any of the lines.

Unfold the shirt and cut until your scissors meet the edges of both lines.
Repeat this step in between all of the lines.
Don't worry if your strips are not perfect. If you are using a regular cotton tee, then the strips, after you wash the shirt, should begin to curl around themselves a little, which should disguise any imperfections.