Seal windows and openings
In college, we were unlucky enough to get the bed closest to the window. During winter, the cold air seeped through the cracks, and no amount of blankets could keep us warm. However, this can also become a problem in summer.
Warm air can come inside and bring the temperature up. This means the cold air will escape faster, and your A/C will have to use more energy to cool the house down. Fortunately, sealing any openings up with caulk should solve that problem.