Purchase and hang white window shades over all the windows in the room. White reflects sunlight and the shade material will help absorb some of the heat that would otherwise enter the room.
Hang curtains over the windows. Combined with the shades, curtains helps keep the room shaded and cooler. Keep the shades and the curtains closed during daylight hours, when the sun is streaming in the windows.
Run at least one fan in the room to circulate the air. This will help whether you have an air conditioner or not.
Keep the room's interior door open to allow a cross-breeze from other rooms, unless your room contains a window-unit air conditioner. Closed-up rooms, without air conditioning, get hot and stuffy.
Open windows partway on cool nights to allow cool, fresh air inside. Place a fan in front of the window, and facing the interior of the room, to draw in cool air from outdoors. Turn off the fan and close the window in the morning, before outdoor temperatures rise.
Turn off all unnecessary electronic equipment when they are not in use, including computers, lamps and other devices, which emit heat. In addition, turn overhead lights off in the room when it is not in use.