There are several things that you can do yourself.
Once a month, (depending on use) clean your unit's glass on both sides with a glass cleaner.  Failing to do so will result in your glass becoming "cloudy."  If left unchecked (and uncleaned), the glass can become permanently etched with this "cloudiness." While you're cleaning the glass, check the gasket that is on the glass door or on the exterior around the firebox.  Any gasket that is either cracked or missing pieces should be replaced immediately. Then check all of the wing nuts, bolts, etc. (whatever is being used to keep your glass door in place) to make sure that the glass door is fitting securely.  If the glass door is not secured tightly or if the gasket is cracked and missing pieces, carbon monoxide can escape into your home.  Then, visually check out unit's outside vent.  Make sure there are no leaves or nests in the vent and replace the vent kit if it is torn or damaged in any way.