When you are on vacation, your home is most susceptible to burglary. One trick to create the illusion that you are home is to put a few lights on a timer. Individual timers can be found at the hardware store. Program the individual lights to turn on for a while each night. It's also a good idea to have someone visit your house every couple days to make sure mail, newspapers, or packages aren't piling up.
If you live in the snowy states, have someone drive in and out of the driveway a few times, and if possible, shovel the sidewalk, even if it's only a small path.