Step 1: Supplies!
A t-shirt or other cloth material
A bleach pen
A magazine/cardboard/plastic bag
A water source
Step 2: Insert protective lining
Step 3: Draw!
Draw! I just freestyled a griffin head, but you can use chalk to lay down a pattern first for more control. Anything you draw on the shirt will leech a little bit and your lines will be about twice as thick as what you draw.
Watch your fabric. It begins to whiten almost right away. I let this one sit for about ten minutes before moving on to the next step.
If you plan on drawing a big pattern plan to do it in batches. Draw, move onto the next step, and come back to draw some more later. Otherwise parts of your lines will not have the same lightness. You can always come back and do more, but you can't undo anything once it is done.
Step 4: Wash
Wring out the shirt and rinse again to make sure all the bleach is gone.