I used a Cricut Explore Air 2 for this project, but any vinyl cutter should work just fine. I've added a link to the project on the Cricut Design Space so you can customize the design or the message to match your style.
Or, you can download this image file for use with other vinyl cutters or vinyl cutting services.
Different sized t-shirts will want different sized designs. Luckily, it's easy to customize the size in the Cricut Design Space. Just select the group and drag the corner until it's the size you want.
Next, select all the layers except the circle "moon", and click "Weld". This will ensure the whole design cuts as it's laid out on the design board.
Do a test cut on a sheet of paper or card stock and hold it up in front of your shirt to be sure you like the sizing and placement.
After you're sure you're happy with the layout, load your iron-on vinyl into your vinyl cutter liner side down. This means shiny-side down, or upside-down, most of the time. Double check to be sure you have this right! This stuff is expensive.
Set your vinyl cutter to the "Iron On" setting and cut.