Spoonflower recommends that one washes the fabric first. I do that and then hot dry it to set the image. Haven't had any problem with the image fading so far (3 years).
Responding to tropit - I did not design the bunny image. Spoonflower has a great search engine - just type in what you want, i.e., cats, flowers, dots, squares, science, etc. and hundreds of possibilities come up. You can choose what type of fabric you want the image printed on. I recommend them highly.