Don't leave your holiday lights on when you leave the house or when you go to sleep. There is always the possibility of a fire so it's best just to turn them on when you can enjoy them.
Make it a holiday tradition to change the batteries in your smoke detectors. You'll keep your family safe and having lots of people around could make a boring task into a fun family tradition.
Make sure you regularly water your live tree. If there is a fire, a well watered tree will not burn as readily as a dry tree.
(An NFPA video comparing the two)
If you choose to have an artificial tree, make sure that it is labeled as fire resistant.
Only light a fire in your fireplace if the chimney has been cleaned this year by a professional. The creosote that builds up in your chimney is highly combustible, especially in large quantities.
There is a lot of cooking going on during the holidays. Remember to wash your hands and cooking surfaces regularly. It is a good way to prevent the flu and food borne illness.