Whenever you go outside, lock the door and take the key with you, even if you are just stepping next door or out mowing the back yard. Do not leave it open when you are away, an empty garage broadcasts your absence. When you aren't home, use a timer set to turn interior lightson and off at varying intervals as though your home was still occupied. If someone comes to your door asking to use the telephone, make the call yourself. Don't invite them in.
Thieves know all the good hiding places.
Trim back any trees or shrubs near doors and windows to eliminate hiding places for would-be thieves. If you own a dog and go out of town, have someone come in and care for your dog in your home. Videotape the contents of your home. Keep the video and the list of all valuables in a safe place, such as a safety deposit box or fire safe. Don't invite them in.