Step 1: unfold your tissue paper all the way
Step 2: I cut mine in half so the finished product wouldn't be so huge.
Step 3: Fold them into an accordion fan shape like the ones you made when you were a kid. Then wrap wire around the middle.
Step 5: fan out both sides as much as you can
Step 6: carefully (this is important because the tissue paper tears easily) pull up on each layer until it forms a pretty ruffly hanging tissue paper ball. You might have to play with the layers a little bit when you are done to get it to fill in all the right spots.