Pick someone you admire! (Pic #2 is the one I used for my stencil).
This is my dad's pink, faded t-shirt from the 80's which he gave it to me in a box of old clothes. One of my many idols is Freddie Mercury so I made this shirt as a tribute to him. His signature is on the left shoulder which I found online and copied in paint. This requires basic silk-screening by hand. It took me some trial and error. Also, my perspective on the first picture is bad, it does look like him but the shirt has wrinkles.
First find a good t-shirt. Mine has lots of character to it. There are bleach stains, holes and general rattiness on top of fluorescent pink. I actually hate pink but this is an exception.
Find a good picture of your idol online and blow up to a good size (enough to cover at least a third of the front of the shirt). Turn to black and white and mirror using iPhoto, Photoshop, etc. Print out.
Trace onto the vellum, which you can find at scrapbook or craft stores for about 60¢ a sheet. Mark the parts of the photo that are black or very dark gray. You'll need to cut these out and leave the rest. This part is tricky, especially with eyes. Sometimes you need to leave white parts and hold them in place as you paint.
Put the stencil where you want it and paint over/around it. Hold it in place with your fingers while you paint.
Let it dry and add any other details such as words, lyrics, etc. Leave it overnight. Now you're done!