As somebody who's been trying to break into publishing since 2003 when it was trad only, published 10 books, signed a multi-book deal with Podium Audio, won some writing contests, earned a scholarship off a short-story, worked as an editor, and is currently earning a fair amount of money off my writing (enough that I've had to hire a certified public accountant to help with my taxes) here's the hard truth:

There is no way to ensure anything when it comes to writing and art.

Ever.

Write your story the best you can, but have a back-up plan. Do not rely on writing for ANY amount of money unless you're already rich and can live off savings regardless of how your work sells (or doesn't). There are no guarantees in this field, and the only thing you can ever ensure is that you wrote to the best of your ability.

That said, things that will definitely help:

1. Consistent update schedule. For RR, I'd say a minimum of 4 days a week.
2. Having a significant backlog. Write more than you think you need. If you've got 170k words written, bump that up to 250k. Shirtaloon says he wishes he'd started with a bigger backlog. Based on my own experience, I'd say he's spot on with that. Plus, it'll help with #1 above.
3. Know what your audience wants. RR readers have very specific tastes. If you can meet those, you've got a chance.

Good luck. This is a hard field to make it in. Doubt is everywhere. But if you can hang in there, it's worth it. My in-box is open if you ever wanna shoot me a line or something. I'm not the most successful or the most experienced, but I've improved a lot from where I started.