First, I bought a basic apron from the craft section at Walmart.
Then, I found a pumpkin carving stencil online. (Found here.) He has been super into Star Wars lately, so I thought a Storm Trooper would be fun. I printed it onto freezer paper.
I taped it down so it wouldn't wiggle while I cut, then cut out the black areas with an exacto knife.
I then positioned the stencil where I wanted it on the apron and ironed it on (shiny side down). Make sure your iron is hot enough that the stencil is tightly stuck. The first time I tried this (craft fail!) I didn't iron it well enough and paint seeped underneath the edges.
I put on a couple of coats, until it didn't look pink anymore. When it was nearly dry, I peeled off the stencil. I let the paint dry fully, and then I ironed over it to set the paint. (I have no idea if that is even necessary, but I figured it couldn't hurt.)
I think the Storm Trooper apron turned out really cute. It's perfect for my boy.