It depends upon your ceiling fan.
What you are looking for is a motor that has permanent magnets in it; a lot of AC motors 'around the house' have coils which energise to form the magnets and these won't do.
Basically, if you put a volt meter across the wires which would normally power it, spin the motor, and it shows a voltage, then it's likely that you're on your way to generating something.
Slog (fellow newbie)