Common mistakes when making cinnamon rolls include overheating the liquid that activates the yeast, overworking or under-proofing the dough, using incorrect ingredients like expired yeast or low-quality butter, packing the rolls too tightly in the pan, overbaking, or failing to add enough moisture to the dough. These errors can result in dense, dry, or flavorless rolls, so paying attention to temperature, proofing, ingredient quality, and baking time is crucial.