You can tell by looking at the selvage edge of the fabric, take a close look at the little holes that are left by the sprockets on the winding machine, usually you can tell the right side of the fabric when the tiny holes are smooth and go downwards into the fabric, the wrong side has a slightly rough feel where the holes push out/up a little bit! Hope I am explaining this properly, if not perhaps I can send in a pic. This is the general rule of thumb for cotton fabrics plain or patterned.
Gal