The first thing you need to buy when you want to make a stencil for a T-Shirt is some acetate. Acetate is widely available on the black market in Prague:), as well as most Art stores. Here I am buying some acetate from a local supplier (who also happens to be my friend, Jana) Other supplies you will need include a foam roller, a little tub for the paint, a big sturdy box on which to cut your stencil, and a razor blade (exacto knives work really well)
Using a google image search, I found this picture of Christopher Walken which I thought would look good as a stencil. Plus my ex-girlfriend/Bestfriend Andrea is a big supporter of the Christopher Walken Presidential campaign for 2008. I also owe her a present, because she made me some rad pillows, as well as sent me a bunch of vitamins for my birthday last year.
Using photoshop I have taken the contrast and brightness way up in order to make a black and white image that lends itself to making a stencil. In Photoshop, go to "Image" then "Adjust" then "Hue/Saturation", take the saturation all the way down in order to make the color picture a black and white image. Then go to "Image" then "Adjust" then "Brightness/Contrast". Play with the Brightness and Contrast until the image begins to look the way you want it to.
Tape the acetate on top of the printed image. Make sure both the paper with the printed image is securely taped down, as well as the acetate on top of it. Acetate, or the paper moving will cause your "trace cutting" to move, and make you lose your place.
Using a razor blade, I trace the original image, and begin cutting out the stencil. Make sure you don't cut out an entire area that needs to stay. Your stencil needs to be strong, so, when possible, don't cut some areas that are black in order to reinforce it.
using a foam roller, I apply the paint over the stencil, making sure not to have too much paint on the roller. Having too much paint on the roller will cause the paint to get under the stencil, and cause splotches. With practice you will find the pressure needed, as well as how much paint to load up the roller with.
The finished product. One could generally see the stencil better if one used darker colors, however I decided to use a lighter color in order to be a little more subtle, and create a better match with the existing pattern of the shirt. Plus guys who wear pink are generally pretty cool.