Check your chimney periodically from the outside to see if you see any cracks or gaps in the joints. These often become stained by smoke, making them easy to see.
Make sure you have working carbon monoxide detectors in your home, preferably on each floor, and particularly in sleeping areas. These can indicate a venting problem. Check them regularly to be sure that your family isn’t exposed to even low levels of carbon monoxide.
Keep your fires burning nice and hot to prevent the buildup of creosote in your chimney.
Schedule an annual cleaning and examination of your chimney and flue with a chimney repair professional. If you use your fireplace or stove regularly, these checks should be even more frequent.