Draw out your design on poster board, first in pencil, then in fat marker. Use a new t-shirt or look in dad's closet. I'm sure there are 100s in there.
Insert design into a t-shirt. If you can't see the marker lines showing through, dim the lights or shut the curtains.
Using a stiff, short bristled brush, paint on design with fabric paint.
Work from top to bottom. Go over it a few times if needed. Let dry. Iron shirt with a piece of fabric over paint to set the ink (or follow directions on your paint bottle).