Haha, one of my earliest jobs was in a laundromat, and I was taught by the master how to fold fitted sheets!
It's pretty simple - you put your hand in one corner, and fold the opposite corner from the bottom end over it, then you do the same on the other side. Once you have that done, you fold the sheet in half lengthwise, and put one corner in the other, then lay it down and fold over the corner and the part of the length of the sheet that is as wide as the corner. From there, fold it again lengthwise, then crosswise, and, voila!