So, you want to be a writer?
Maybe not, but keep reading, you might be entertained.
The first rule that many people tell you in creative writing is "Write what you know."
I'm going to tell you that this is the last thing you should do.
No one wants to read about your family drama. Do you think that Vince Flynn is actually a terrorist hunter? Or that Bob Kane dressed up as a giant bat? Or that Stephen King is a demonic clown?
Okay, demonic clown is redundant ...
Saying "write what you know" is as ridiculous as suggesting that I am either: an athletic mercenary with enough weapons to take Latin America / a soccer-playing Vatican Secret Service agent / or a commando priest.
I would recommend, generally, that you write what you read. Unfortunately, your writing will probably suck at first. Keep writing. It will still suck. Do it again. Repeat until you no longer suck. Trust me, I speak from experience. And from the experience of Timothy Zahn, John Ringo, and several other authors who discovered how to write the hard way --by writing.
That would lead to an obvious follow up: read. No, Vince Flynn is not an assassin, nor am I any of the above.
However, we all do research.
For my novels I read easily a dozen books worth of material. We will not include all of the various and sundry newspaper articles and websites and lectures that I had to go through to collect information on weaponry that I've never held, and tactics I've never had drilled into me, and places I've never been. And we can ignore the fight scenes I had to rewrite after taking 18 months of self defense training.