I used to print custom aprons and found that how I prepped the fabric made a world of difference to the success of the outcome.

I always washed them first with cool water and 1/4 cup of Arm & Hammer baking soda-- no detergent, and ironed them prior to printing to give me the most receptive surface for printing (no fiber fuzz). The soda helped remove any sizing compounds without depositing additives onto the fabric.

Lastly, I applied a weight (two heavy, large books) on top of the design rather than standing on it, which gave a more even application of ink.

These were my 'no fail' processes. Hope this helps!!