My first pizza stone broke when preheating it in the oven. I got it at a thrift store with no instructions. After that, I got another one, new. I am afraid to preheat it but upon reading all the given info, I am encouraged to do so again. I just don't want to lose my expensive stone. It does seem it should make a better product if preheated. Are there any pointers or don'ts that should be followed for preheating?