How do you know which is the right side of some fabrics? I think I read once you could tell by the pin-holes on the sode of the fabric from the looms. I'm working with a fabric at the moment for the childhood challenge which has very subtle differences on either side. Will probabaly lay the whole lot in one go with one side up. Just lie to hear what others have to say though.
What kind of fabric is it? If its not printed and it's just a plain weave, there is no right side. If this is going to be a problem, I would put X's in tailors chalk on the side you decide is the wrong side.
If I remember correctly the right side is with the punctured bits of the pinholes facing up. But ultimately, if you like one side more than the other go with that - just remember to be consistent otherwise it could look weird in some lighting.
You can take a look at the selvedge edge and look at the puncture marks... here's Sewing With Nancy's Tips (scroll to the bottom)