Tutorial: DIY Tissue Paper Pom-Poms this tutorial is pretty good. Use square sheets or tissue for a rounder Pom Pom. We tied the middle with ribbon and tied several on ribbon and hung them for a backdrop. Use thin tissue paper and fluff gently.
How to Make Tissue Paper Pom-Poms in Different Sizes
Great tutorial for how to make tissue paper pom poms also includes a Tissue Paper Pom Pom Size Chart. It tells you how many sheets to use for each size pom pom as well as what size the tissue paper sheets should be.