Water Heater - Before you leave for your vacation, set your water heater to its lowest temperature to save energy. Some of the new models you see today even have a 'vacation mode' and wireless controls. If you're being conscious about going green and avoiding wasted electricity, this is a great (and easy) thing to do.
Thermostat - One thing I have always done is adjust our thermostat so that it is closer to the outside temperature. No need to waste a lot of electricity by keeping your house as warm or cool as you normally would when you are at home! Of course, this should be done with weather extremes in mind. If you are heading away when the outside temperature is near freezing, you want to keep the house warmer so that your pipes don't freeze.
Electronics - Unplug electronics from wall outlets or use surge protectors. This is good to do to avoid electrical issues and any potentially unwelcome surprises when you get home.
Mail - You can arrange to have the mail held at the post office while you are away so that it doesn't pile up. You can also look into a mailbox with built in storage so that your mail will be kept secure and won't overfill your box (a sure sign to passersby that you are away from home.)
Social media - Resist the urge to post all over your social media that you are heading out of town. I see this ALL the time. "Joe Smith is flying to Tahiti from JFK," or posts saying "2 weeks on the beach here I come!!" Sure, your friends will enjoy the posts but it also makes it very obvious to strangers that your house is (potentially) empty.