Indoor Flight:
Make sure that you are not in a crowded area -- even the best of pilots can lose control and the blades of a helicopter can really hurt someone. Make sure you have enough room to maneuver around furniture and hanging obstacles (fans, lights, etc.). Be sure there is enough turning room to avoid crashing into walls and damaging your aircraft.
Outdoor Flight:
Make sure that your operating area is free of power lines and trees. The last thing you want after dropping a lot of money into your RC plane / helicopter is for it to be fried by a high-voltage wire or for it to tear itself apart in a tree. Avoid flying over crowds or vehicular traffic - you don't want to crash into people or cars.
