If you choose to use your own fabric, it must be washed well with a plain soap, no softener. I would even add some vinegar in the wash and rinse cycles. You don't want any chemicals in the fabric when you print it off.
You may also want to purchase a bottle of Retayne to treat the fabric after it is printed, no matter which method you use. This will help to set the ink into the fabric.
If you have a print company in your area, they may be able to do this for you. You can call and get an estimate on their fees.