Where you place the fan depends on whether you have cooler air available.
If it is hotter outside than inside (so you can’t get cooler air from outside), you should place the fan so it blows on you, horizontally. You don’t want to blow the hotter air from the ceiling down, nor do you want to blow the cooler air near the floor up (because this will also pull the warmer air down).
If you have cooler air outside, put open one window on one side of the room for incoming cooler air, and open a second window for exhausting the warm interior air. Put the fan in the exhaust window pointing out. This may seem counter intuitive, but by blowing out you are assuring the hottest air is being pushed out. if you push in, the air in the room resists moving, the pushed air hits this resistance and some of the new, cooler air goes back out the window. When blowing out, there is no such resistance and all the hotter air goes out.