Create two small pattern pieces to dictate the shape of your cut-outs on cardstock. It can be arbitrary, but check the neckline you're dealing with to see what shape works best.
Lay pattern pieces down on Tee, creating a motif. Start from the center of the neckline and trace off with something wash-able. Doing this from the inside of the shirt to avoid marking it permanently is also a good idea.
Continue until you've achieved your desired motif. We like rotating the two shapes along the contour of the neckline to give it some geometric allure.
Once your motif is traced off, carefully cut out your shapes.
Don't stress the garment too much once you've made some holes in it - it will be delicate unless you're working with very thick material or some sort of reinforcement.
Finally, roll up the sleeves to form a stylized cuff.