For maxiumum window clearing power...
Push the button on the far right for the defroster vents.
Push the button for bringing air into the vehicle (not the recirculator).
Put the blue/red slider all the way to the red.
Turn the fan up all the way.
Turn the AC on.
The AC coil sucks moisture out of the air then the heater warms it back up. Warm dry air = clear windows.
If you're in a region with snow, the air intake vents under the windshield wipers can be covered with snow. Be sure to brush those off. Anything that falls into them is going to get sucked into the system and come out as water vapor onto your windshield. When I know its going to snow, I pull the 2nd row floor mat and put it carpet side down over the vents. If the wind is blowing hard, put it under the wipers too.