first find a simple base idea to help u draw out the skull
now draw a simple outline of the skull on the shirt: the head, eye holes, noese, teeth marks, and cross bones. make lines about 1/2 to 5/8 and inch apart goign across. maek sure NOT to draw cutting lines over the eyes nose or teeth. if you do this u might accidentally cut those off.
now slowly nad carefully cut along the lines. if u did it correctly u should have a bunch of slits that make the shape of a skull with areas for the nose eyes and teeth left. layer it over another shirt and enjoy