Don't Do This:
Don't refigerate your shisha tobacco, it adds too much moisture content and it "shocks" the exact mu'assel mix of honey, molasses, tobacco and glycerine binding.Some say to put an inch of water in the bottom of the bowl and sticking it in the freezer. I've done this and had a cracked vase from the result.
Better to put ice cubes in the bowl with the water... or buy a "chiller" hookah that has an ice metal vase at the top of the shaft underneath the clay shisha bowl. You can even buy the vase separate and add it to your existing hookah.
Don't pack too much shisha into the bowl - it stops air flow in the clay bowl, heats, and burns.
Don't suck too hard on the hose - it also heats too quickly the tobacco.
Don't use too much coal, it burns the shisha, makes it harsh. Try breaking a coal in halves.