1. Close Your Windows
It may seem counterintuitive, but on hot summer days, opening the windows will often make your home warmer, not cooler. Open your windows only at night if the air outside is cooler than inside, and close them along with blinds and shades before the sun hits your house in the morning. When night falls, open windows wide, particularly those oriented toward prevailing winds so you can take advantage of cross ventilation. This will allow cool night air to circulate, and prevent a good deal of the sun's heat from reaching indoors. You may also put houseplants particularly larger potted trees in front of sunny windows to absorb some of the sun's energy.