A few days ago was our anniversary (3 years!) and I made Adam this T-shirt as a little gift (it is a college basketball thing). I love decorating shirts with freezer paper stencils. It is so easy.
1. Print or draw design on the paper side (as opposed to plastic-coated side) of some freezer paper.
2. Use a utility knife to carefully cut out design.
3. Lay out T-shirt with a piece of cardboard between the layers of fabric to keep the paint from bleeding through.
4. Position the freezer paper stencil on the T-shirt, plastic-coated side down, and iron it. Use the hottest setting appropriate for your fabric and make sure the stencil is stuck securely to the shirt all around the edges of the design.
5. Using a medium or large brush, stipple your fabric paint all over the stencil until it looks completely opaque.
6. Let the paint dry completely and then carefully peel the stencil off the T-shirt.
7. Heat set the paint by ironing on the reverse side of the fabric. I like to put a piece of cardboard between the shirt's layers again just in case I missed a damp spot in the paint or something.