Like most of the responders here, I usually only use a hot towel when I do not shower before my shave. But, every now and then I like to do a combo shower and towel then shave.
What I like to do is run a sink full of steaming hot water, soak the towel, put my mug in the water to submerge it about half way, then I cover my mug with the wet towel. If the water is hot enough and the towel is thick enough, the towel will trap a lot of the steam and keep your mug nice and toasty. You'll know if you did it right, because when you get out of the shower the towel will be swollen up like a balloon over your mug. When you take it off a puff of steam should come out and a hot mug and steamed towel will be ready to go.
What I like to do is run a sink full of steaming hot water, soak the towel, put my mug in the water to submerge it about half way, then I cover my mug with the wet towel. If the water is hot enough and the towel is thick enough, the towel will trap a lot of the steam and keep your mug nice and toasty. You'll know if you did it right, because when you get out of the shower the towel will be swollen up like a balloon over your mug. When you take it off a puff of steam should come out and a hot mug and steamed towel will be ready to go.