Raise your ac thermostat in the summer time. You can still keep comfortable without being too cold. The more the ac runs the higher your electric bills will be.
Close blinds to block out the sunlight and keep the heat from getting into your house.
Turn off lights when you don't need them. Avoid baking anything during the hottest part of the day. The heat generated from your oven will heat up your house making your air conditioner work harder to remove the heat.