As we get into the heat of the summer, realize that most nights are still cool enough to sleep comfortably.  Warm air trapped in your house may make you disagree.  So what to do about it?  Open two windows on opposite sides of the rooms you will be in.  This allows air movement, providing cross ventilation which will make the apparent temperature feel 5-10 degrees cooler.  Just make sure you turn off your HVAC system or adjust it to the fan only setting to save on energy costs.