I was working part time as a waitress (4-5 nights/wk) when I started working as a massage therapist. So I'm afraid I'm not exactly the example you're looking for. But I will say that there was never a point where I thought "okay, I am now making enough money doing massage to support me, I can quit my other job." I came to the point where I said, well, it looks like there might be enough massage out there that if I devote myself to it, it will support me.
Also, I have in control of my living expenses, having no dependents, so I have never had to support anyone but myself. But there was a moment when I had to take a leap of faith and free up the other areas of my life so that more massage could come in. And it did.
What I did was work at a Day Spa during the days, and worked waitressing during the nights. It took me only about 5 months after graduating massage school to quit my waitressing job.
I think the best way to promote yourself is to do fantastic massage and get people requesting you (if you mean promote yourself at the spa, and not at a private practice). Also, become well-known for "fixing" people. I have always loved working on issues and pain, so I would talk about it a lot at the spa, or when a client left who I really helped I would mention how I loved to work with those types of people. Soon, I became known as the go-to person for people who came in with pain and I wound up getting a lot of requests.