Hang up blackout curtains. Blackout curtains are dense and heavy, and will stop light from coming into a room. Monitoring how much sun comes into your house will help you modulate the temperature.
Identify the south- and west-facing parts of your house and keep those windows closed during the day. These are the sections of your house that receive the most sunlight and heat during the day, so closing your windows and keeping the heat from pouring in will help make your house a little cooler.
Point box fans to blow out your windows. Box fans are made to sit on your windowsill. If you position them to blow out the window, they will suck out the hot air from your house and deposit it outside.
Turn off appliances you are not using. One of the biggest conductors of heat in a house is the appliances, and shutting them off when not in use can help keep your house cooler.
Warm a cold house by baking or broiling in your oven. Bake bread, make a pizza or broil meat to raise the temperature in the kitchen and surrounding rooms.