This quick safety check is a must for preventing fires -- even if you haven't planned on starting any fires soon.
Take a flashlight and peer up into your chimney's stack. Look for debris, soot, or white streaks. If it's clear then you're all done. If you do see buildup, this is a great time to call a professional. It can potentially be cheaper to hire a chimney sweep in the offseason as well.
If you have recently used the fireplace clean your wood burning fireplace's interior, including its floor, regularly. Sweep out or vacuum up cold ashes. Wear a dust mask and gloves when cleaning the fireplace.