Cut the sleeve rectangles (from a nude-colored, sheer nylon fabric) wide enough to go around the T-shirt's sleeve and long enough to hang from the bottom of the shirt sleeve to your wrist. Add in a 1/2 inch to all sides for a seam allowance. Now taper the long sides of the rectangle, so that the rectangle's sides slope inward. This is so that one side will fit cleanly around the end of the shirt sleeve while the other is narrower, to fit better around the wrist and forearm. After measuring the widest part of your forearm and wrist, taper the sides according to the size of your wrist and forearm.
Look at other tattoo sleeve designs for ideas. Classic designs include tribal patterns, Celtic patterns, and the more ornate Oriental designs incorporating dragons and clouds. How elaborate your design becomes will be determined by your artistic abilities. For a first attempt, a tribal pattern will probably be the easiest.
Mark the design on the nylon fabric using a pencil. With a tribal design, use bold lines that curve, intersect and end in points. Although the two sleeves do not have to match, if you can make them mirror each other, it will look more balanced. After drawing one, flip it over for a mirror image and place the second piece of fabric on top and copy the image in reverse.
Paint the design using fabric paint. All the design to dry thoroughly before sewing the sleeves together.
Sew the sleeves. First turn under the wrist edge and sew the band, creating a neat (raw-free) edge. Then fold the sleeves so that the painted side (the right side) is together and sew along the long side, creating a sleeve. Now turn the sleeve inside out. Now the seam is on the inside. Lastly, pin the top of the sleeve inside the T-shirt's sleeve and sew it in along the T-shirt's visible seam line.