if you use AC insulate (minimum 4 inches) the attic floor (interior ceiling), put a thermostatically controlled fan at one end and an intake (non powered) at the other. Size the fan based on the volume of the attic to give 6-8 air changes per hour. If you do not use AC put a large ceiling fan discharging into the attic and make sure there are vents in the roof or gable to let the air out. If you do this you have to have screens on windows. Be aware that with this your house will be about the same temperature as the outside air and or rainy days the inside humidity will be high.