It's a simple, old-fashioned practice. Close south and west-facing curtains. Do this during the day for any window that lets direct sunlight in. Keep these windows closed, too. Another good, old-fashioned solution is to install awnings.
Awnings work best on south-facing windows where there's insufficient roof overhang to provide shade.
Canvas awnings are more expensive than shades, but they stop the heat on the outside of your building, and they don't obstruct the view. Hang tightly-woven screens or bamboo shades outside the window during the summer. They'll reduce your view, but are inexpensive and stop 60 percent to 80 percent of the sun's heat from getting to the window. Deciduous trees block summer sun, but drop their leaves to allow half or more of the winter sun's energy to warm you on clear winter days. Low-e films block most solar heat gain while transmitting most visible light.