...master of none.
Yup, that's us as writers. Good writing requires us to draw the reader into our world, but how can we do that when we haven't exactly been there or done that. Another great advise from Anne Lamott is just ask.
Don't know how to plant a garden? Go to a nursery and ask. Ask away. Plant away. And keep asking how things should turn out under which conditions. Paint that distinctive picture with words, movement, and attention to detail. People like talking about their occupation. Use it.
Did you know that civilians can do ride-alongs with cops. I haven't tried this one recently. But it's great material to get a feel for the life without living it. And again...ask away. Take in the visuals, the smells, the emotions. Check out procedures and attitudes of your fellow protectors.
Of course there will be limitations. You can't experience everything, but you can take enough of what you need to get things started and to make them yours.
Fantasy and Sci-Fi folks, tread with caution. You can use real elements mixed in with the fantastical.
So...ask away. You will write better for it.