I found this great article about how to start your t-shirt business.
Maybe you are interested.
"If you are about to start your own t-shirt business, establishing
your priorities and goals has to be your first step, because it will
guide your business in a certain direction and it is important that
you do NOT abandon these guidelines."
You can read more about it here:
http://www.tshirt-designs.com/blog/priorities-and-goals-when-starting-a-t-shirt-business/