I chose a design first. I used a rose of sharon quilt block design from one my books. I prepped the shirt by removing cat hair and lint, and placing a large piece of cardboard inside the shirt to protect the back of it from getting bleached. I traced a square ruler on point to mark out a space, using a white chalk pencil, which will wash out easily.
I freehanded the design with the bleach pen. I have a lot of experience doing this sort of thing. I used to make ceramic ornaments and I decorated them with liquid slip (clay), and I have made a million cookies decorated with royal icing and a piping bag. If you are not confident with this skill, just use the chalk pencil to draw before bleaching, or trace the design on a lightbox. You could also perforate the lines of a drawing on paper and use loose chalk or baby powder to pounce the design onto the shirt.
Despite being fairly confident freehanding the design, I would do a lot of things differently next time. First, I would buy two bleach pens. I went through almost a whole one on this design. I would hate to run out of bleach mid-project. I suggest shaking the bleach down into the tip of the pen and trying it out on a paper towel to get out any bubbles. Work as quickly as you can so the bleach doesn't spread too much, and the application over the whole design looks consistent.
Let the bleach sit on the shirt a few minutes while you prep your washing machine. Start a medium load with cold water. I rinsed the majority of the bleach off in the sink. Be careful moving the shirt from the workspace to the sink. If you wrinkle it up the bleach will get smudged. Next time I will used a piece of plastic inside the shirt instead of cardboard so I could keep it in the shirt durning the initial rinse.
I threw the shirt in the filled washing machine, and machine dried it. I like the result, despite the messiness. This is far from an exact science. I plan to work more into the design with thread or paint or both. Stay tuned for the next phase!
