I used to play music as my sole source of income. I was a freelance jazz bassist primarily, but I played some rock gigs and musicals upon occasion. The most important thing for me was to be versatile. If someone called me for a gig, the worst feeling in the world was having to say that I couldn't play in that genre, so I made sure I never had to say that. I practiced as much as I could (sometimes this was difficult due to injury, but I'll get to that later) and I played with everyone I could. Not just for pay, but sometimes for experience and a lot of time for the chance to get my name out there. Reputation is really everything, especially if you're playing freelance.
I rarely had a weekly gig, which meant that someone had to specifically think of calling me when they needed a bassist often enough for me to be able to sustain myself. So, pretty much every gig was not just work, but also a job interview for the next gig. That's the way it is with bands, too (rock bands, at least), because you can't rely on steady employment. Networking is key, too. Whenever I went to see a show, or to a restaurant where a jazz band was playing, I would have to talk to the guys playing just so they either remembered me, or got to know me if they ever needed a bassist. It's that last part which is the main reason I got out of the business and am now a simple graduate student. That and it was a big hindrance to trying to have relationships.
I guess I miss playing jazz a lot (all I get to play is rock, because I don't have a reputation in the jazz community in this town), but it's much more relaxing hanging out with musicians these days. I also don't get to practice nearly enough (only about an hour a day), which is slightly depressing, because even if I got called for a jazz gig, I probably wouldn't be able to play it. I guess this was a lot more rambling about my previous career, but maybe it'll be a bit useful in the discussion.