1) The first thing you can do is install solar screens. We're not talking about the big solar panels that you put on your roof; we're talking about solar screens, also called sun shade screens. You install them on the windows that get the most sun. They're kind of like insect screens, but they're made of a very dense mesh that blocks heat and light.
2) Window awnings also work well to block the sun. The same goes for shutters or roll-up shades. You can buy inexpensive roll-up shades made of bamboo or vinyl strips that will block heat. Hang them outside windows on the sunny side of the house, or you can also hang them over the exterior of the home's warmest side.
3) It's important, and people ignore it, but service your AC unit. If you keep running your air conditioner at maximum efficiency, you can keep your energy bill down as energy bills are expected to grow about 2% a year through 2040.