There are a wide range of trivets on the market. Trivets are designed to keep a surface from being damaged when you need a spot to put a hot pot or dish, although I have been known to fold up a dish towel when I was in a pinch.
Over the years, I've tried a number of them and found my favorites have about an inch of clearance from the bottom of the trivet and the bottom surface.
It also helps if the trivet itself has an open weave pattern so it can quickly dissipate heat. When not in use, you can also use trivets to add a little decorate charm to a flower pot!