Always leave the windows cracked about a half inch. The car won't get quite as hot inside. It will still be hot, and hotter than the outside air is, but not as hot as it would be if the windows were up all the way.
I agree with the window folding shades for the front and rear, if you have those sorts of windows (I drive an SUV and the back window is vertical, so those do nothing).
I also will roll the windows ALL they way down immediately upon starting the vehicle, and turn the a/c on high. It makes it easier for the car to push the hot air out of the vehicle if the windows are down. As I start to drive, I let the a/c blow high and the windows stay down for a minute or so (if I am moving steadily, not pulled out a car length and stopped at a stop sign), then put the FRONT windows up and leave the back ones down for another 15 seconds or so. Then put all the windows up and turn the a/c to recirculate.