"Write What You Know"
What kind of advice is that? I know it's come out of the most famous, popular and award winning authors since the beginning of time but ... I have to disagree. (non-fiction being the exception) What if what you know isn't interesting? What if you feel the calling to write about a race car driver? You're half way there, you've driven a car. The racing part ... you can learn!
There are no limitations to your imagination!
If everyone followed that philosophy of write what you know, we'd never have great works like ... Superman, the Little Mermaid, Journey to the Center of the Earth. You'd have boxers writing boxing literature and inmates writing murder mysteries because who else would admit to have experience in dolling out death? Oops, I think OJ did do that.
Imagination and the internet. That is what you need. So all you science fiction authors who've never ridden on the Space Shuttle ... relax, let out a huge sigh of relief knowing that you don't have to spend a fortune to be a Cosmonaut! You just need a computer and a vivid imagination.
And when you bump into the submission guidelines that ask why are you qualified to write about interplanetary travel know that if not you, who? John Glenn? Pretty sure his was an autobiography.
As the author of a spy series, I'm not at liberty to explain how I get my plot lines and that's what I say in my query letter. What spy is going to lay out the truth just to get published? Besides, who knows ... maybe I am a secret agent! Does it matter?
Take care and write what you love - if you know it, excellent!