Don't quit your day job. As a writer/author, the money you are making from your books now is probably not enough to support you completely. And, if it is, congrats. Any advice you can give the rest of us is completely welcomed. The point I'm trying to make today is: We all need a steady paycheck, and writing may not give us that. Let's face it, many of us have families, and we all have bills that need paid.
Even as a successful author, royalties may not be enough. Anyone familiar with Dorchester Publishing will know what I mean. Author Brian Keene is all too familiar with this problem, and you can read more about it here if you are interested in learning more about the Dorchester Boycott.
Realistically, your characters should have jobs, too. Though characters are not the main point of my post today, I would like to point out that anything I aim toward writers and people can be aimed at writing and characters, as well. No matter you books setting and time frame, there is always a way to incorperate work. You can find interesting ways to put it in there, too. For instance, you may have a story that takes place on a train, and a man may end up playing an intrigal role in the story because he's a dentist. Why? Well, I don't know, but it would be really neat if it had nothing to do with dentistry.
In the real world, we all take inspiration where we find it. Write what you know is drilled into our heads. Being someone that has had several different jobs, it helps me to think about the differences in all those jobs. What have I had to do in each job? How have I interacted with my co-workers, and customers (if there are any)? How have I felt about my job and does that change on a day-to-day or shift-to-shift basis?
Every little thing can help your writing, but the best thing is to make sure that you are helping yourself. Be it that you take classes to better your writing skills or work a 9 to 5 to afford the utility bills.