Even if you have a camera or security system, it's hard leaving an empty house.
Tell a neighbor or friend you are going out of town so they can keep an eye on your house. Does someone know where you are going and know how to reach you?
Depending on how long you will be gone, have someone pick up your mail (or put it on hold at the post office).
Before leaving be sure to lock windows (and doors) and turn off lights. Do a quick check of the kitchen to make sure all appliances are off. Turn off or set the HVAC to an appropriate temperature. Take out all trash so you don't come home to a stinky house. You might want to put a lamp on a timer.
I do not like coming back from a trip to a messy house, so I'll make sure there are no dishes in the sink, the counters are wiped down and misc stuff is put away. I'll also do a quick pass with the vacuum.