I don't know if this could be emphasized enough! Size your room properly for a ceiling fan. Do not rush this part of the job - take your time and figure out your square footage. Take into consideration the volume of air in the room and how hot / cold it gets. Do you already of windows in the room that can be opened to increase the flow of air? Do you want to place the fan in the center or perhaps at one side to create a directional flow of air?
There is a rough guide available for sizing your room for a suitable ceiling fan. This one was sourced from the Hunter Fan Company.