Are you overwatering? I treat mine really meanly and it is brilliant, have had it for over thirty years!

Would help if I knew what variety of Ficus you're talking about, but as the leaves are falling off, I'll assume you mean a houseplant and not outdoor Fig.
Some leaf loss spring and autumn is not unusual for Ficus benjamina varieties, its the change of season and conditions that cause it. They absolutely hate draughts, and don't like heating much either, so when you first starting using your heating again they can over react and drop leaves. Equally, if its near a window which is open, that's fine all summer, but as the weather cools, the air coming in cools as well and the plant reacts to that.
Water about once a week, sufficient to make the compost moist, keep in a brightly lit spot (daylight) but away from heat sources and in particular, out of draughts - the space between a door and window is not ideal because it would catch any air movement there.
If you have a Rubber Plant, this is not quite so sensitive to these things.