How to properly set-up my air conditioning unit?

Thats about 300 Sq FT. So the unit is designed to handle about 400. If the room is rather hot and its on the upper level floor it may take several days of non stop running to cool the space. If not with in two days (as at night you dont have sun) it cant preform the cooling needs, the unit is too small for the capacity. Meaning you need to add a 2nd unit or buy a larger one. If the other room is seperated by a wall I hate to say but youll never get that room cold. You would need a 2nd unit. Or you can try a small fan to blow the air from the room that has the AC unit feeding it. Again, it may or may not work. The only other option is a portable AC unit which would have a high BTU rating and for sure would handle the space no problem.