This article gives you ways to minimize damage while having campfires.
It says different things, from simply not having a fire, to carrying your own fire pan from site to site. The article gives you advice on what kind of wood to use as well.
I learned a few things from this article but it was mostly just common sense. Things like, don't leave your fire unattended, or don't throw trash into the fire are pretty elementary. Although it had some ideas on how to keep the area clean without making it seem like there was ever a fire in that site.
I would recommend this article to first time campers, otherwise you would probably know these suggestions already.
Allen, Mike. "The Tidy Camper." Canoeroots. Spring 2011. Page 21.