Personally, for reasons I started when teenagers would rummage through the linen closet, I fold the flat sheet, roll up the fitted sheet inside the flat one, wind one pillow case around this and stuff all into the other pillow case. Then I can grab whatever one I want when changing beds.
I tried folding the fitted one after seeing a video of it, then gave up in sheer frustration. I don't need more irritation in my life when the darn fitted sheet flattens out anyway when stretched over the mattress. Who started this flat square stuff..Martha Stewart, I'll bet.