A common piece of advice writers get -- one I agree with only in the broadest of senses -- is to write what you know. Some people take it too literally, thinking they can only use occupations/locations/experiences personally familiar to them. Not so.
An author who's never been shot at can realistically write how it feels. A mother who's never lost a child can write a mother who has realistically. A woman married to a chubby, balding accountant can easily relate what it feels like to fall in love with a tall, dark, mysterious and dangerous spy. All it takes is imagination.
None of my characters are like me. Sure, we have things in common, but the sad fact is, my life is boring (just read my bio; you'll see), and the really sad fact is, I'm high-maintenance. I'm an emotional mess. I'm a klutz of the first degree. I'm allergic to everything. I require great amounts of attention and care (thank You, God, for a husband who can handle it). I'm not the sort of heroine I want to read about, and I think the sort of hero that heroine would require would stretch the limits of believability.
But I don't have to be a heroine.
I just have to be able to relate to one.