1. Find a nice picture without any 'islands'--that is floating white space like the eye in this picture, which I just ignored in the final design. I took this design from dafont.com but if you were actually artistically inclined this would be easy for you.
2. Use an exacto knife on a self-healing mat to cut out the design on your freezer paper. Cut shiny side down. I usually trace the design onto the freezer paper with a pen first but I've also drawn directly onto it when doing the design myself. For this one, I wanted two different sizes of the same design so I just enlarged one more than the other.
3. Iron the cut-out design onto the fabric you want to stencil onto. On about a medium heat. You can check it to see that it has secured. I usually separate the t-shirt layers so that I'm ironing (and painting) on only the side I want paint to show up on.
4. Using a sponge brush and fabric-friendly stencil paint to dab over the stencil. Because the image is ironed in place, you will not have to worry about paint leaking where you don't want it, unless you add water to your paint or something silly.
5. Let the paint dry for 24 hours or more (check your stencil paint directions, really, for anything after this point.). Remove the freezer paper at this point.
6. Iron, with a piece of cotton fabric in between your iron and the painted image, with a dry iron on a high heat (or whatever your paint instructions say to do). Iron both sides of the painted image this way. Also, don't do what I did once, which was to iron both the front and the back of the top in one ironing 'sandwich'. It leaves a yellowish mark on the back of the t-shirt. Iron just the side of the image that you want your image on. This is why I'm using a mini-ironing board in this image.
7. Let it cool for a good while and then wash in cold water and dry on low heat. After this point, you should wash it on medium hot not hot-hot and dry on low, if possible. At the same time, some of these that my sister made I've given a serious baby-tough treatment and they did great.
8. Viola! A custom-embellished top.