To put things in perspective, Columbia, Missouri's Water and Light Department estimates that 50 percent of an energy bill comes from heating and cooling. To combat this, they recommend turning up your thermostat by one degree this summer than years past for a savings of up to five percent on your electric bill. For maximum savings, they suggest setting your thermostat to 78 degrees. This allows the air conditioner to run less, which means you pay for less energy. So whether you live in a house or an apartment, here are some ways to lower your summer utility bills for free :
1. Close the blinds and/or pull the curtains on your windows during the day, especially the ones that are in direct sunlight.
2. Use ovens, dishwashers, and other heat-producing appliances during the late evening or early morning when the outside temperature is coolest.
3. Turn your water heater down to the warm setting, or 120 degrees.
4. Run only full loads in the dishwasher and washing machine. Use cold water as much as possible when running your washing machine.
5. Turn up the temperature on your thermostat before leaving your house or apartment.
6. Wear comfortable and loose-fitting clothes to stay cool throughout the day instead of making your AC work overtime. If you just got back from working up a sweat, a cold shower should do the trick.
7. Make sure all vents aren't blocked.
Hank Coleman of MoneyQ&A.com has a few more suggestions that aren't free, but are definitely worthwhile :
8. Have your HVAC unit tuned up by a certified technician yearly and change its filters monthly. A well-running AC means less money spent on it in the long run and more energy savings!
9. Plant trees and large bushes in front of windows that get direct sunlight to prevent your house from heating up.
10. Have an energy audit done on your apartment or home. The auditor will determine how you can be more efficient with your utilities. For example, they can find drafts where cool air could be escaping and then recommend solutions, such as installing insulation. A common culprit is where you enter your attic. The solution is installing an attic tent that fits over the hatch; you can zip and unzip it to get into your attic as needed. Cracks under your doors could benefit from door sweeps and weather stripping to keep the cool air inside. Most city's Water and Light Departments as well as electric companies offer these inspections for free.
11. Cook outside on your grill instead of on the stove. This prevents heating up your home and thus making your AC work harder.
12. Replace your most used light bulbs with compact fluorescent light bulbs (CFLs). Although these bulbs are more expensive than standard ones, they use 75 percent less power and last up to six times longer than the latter. Replacing two to three of your most used lights in your house with these can amount to a savings of $40 per light bulb over the course of its lifetime.
13. Install a programmable thermostat. Set it to the mid-70s while you are at work, then to a few degrees cooler before you get home. There's no need to be paying for your house to be cool if no one's there.
14. Use more fans, including stationary and overhead ones, as well as your whole house fan if your house is equipped with one. While it may seem counterproductive to use electric fans, they are more cost-effective at keeping your cool air circulating than cranking your AC to a low temperature. It's also a good idea to open your windows on cool summer evenings to take the place of your AC. 
Kimberly Palmer of U.S. News recommends not only turning off, but also unplugging your computer, TV, and other devices that can use power even when they're off. A way to simplify this is to purchase a Smart Strip, which automatically cuts power when devices don't need it. She also suggests taking advantage of the later sunsets and warm evenings to let your clothes line dry instead of using one of the biggest energy suckers in your home - the dryer. 
By taking these tips into consideration this summer, you should be well on your way to shrinking your electric bill.
 Columbia encourages free, easy ways to save on energy bills, KOMU 8
 Ten Ways to Save Money On Your Electric Bill This Summer, Money Q&A
 10 Ways to Reduce Your Summer Utility Bills, U.S. News