Here's my quick and dirty:
Go to school and get a degree in something you can truly use in a number of fields, but find every opportunity you can to kick music courses in there. Get out in the scene and hit jam sessions while you are in school. Network. Offer to record tracks for people. Get familiar with the studio. Use the fact that, if you live on campus, you never have to worry about going hungry or finding a place to crash, or finding a place to rehearse. It can be one of the biggest laboratories for music for you - even if you are not a 'music major.'
I studied Music/Jazz Studies AND Multimedia Arts & Sciences (which got me recording studio experience as well) and helped land the day gig I have now, working in multimedia audio and voiceovers. When I was in school, every elective I could fill my schedule with was music-related. After I graduated, there were other jobs I held that were unrelated in any way to music along the way, but which gave me skills that could be applied to lots of different situations.
I have lived in the same town since college and started out freelancing as an upright bassist (jazz mainly) in the region even before I graduated. That shifted into work with the same steady band I've been in for the past 7 years. There has been freelance/pickup and session work along the way, and I've played in multiple bands at the same time. All of this was while working a day gig of some sort. All the while I have maintained a practice schedule on upright and electric.
Shortly after I got out of school, and a few years into being part of the 'working world' (which meant working 5 days out of the week part-time and gigging 2-3 days on the weekends), when the recession hit I lost 2 day gigs in my field at the same time within 6 months of one another, and gigging opportunities really dried up. It was like that for 2 years or so before I landed the job I have now. But, through all of that, the gigs I *did* have are what helped keep me afloat financially - as did networking connections for other music-related opportunities, and the generosity of friends and family in hard times. What also helped was having a degree that showed I was versatile, and bringing other skills to a band setting as well.
Now, I have a job doing something I like and my main band is doing well. But you know what? I am getting ready to relenquish the full-time bass chair in that band to a friend of mine because they have suddenly want to shift to a full-time touring status. We've made a lot of progress and are fairly well-regarded in the region, and have survived a drummer change about 4 years ago, so I understand why they want to do this (trying to 'MAKE IT BIG' and get more momentum), but I always look at touring from a practical standpoint.
We have been doing it now for the better part of a year and a half and I am already seeing that touring and trying to break into new markets is a financial black hole until you've been to those markets 3, 4, 5 times and have been hitting the road for several years in a row. At that point you ask yourself if it's worth it with all the expenses that are factored in (gas, lodging, food, etc.) and if you really like being away from home and your family that much. I don't. For me, I'd rather return to a multiple-band, freelance setting and control when, how much, and with who I play a bit more and not bleed myself dry on a self-funded tour. We used to make livable money playing locally and within 1-2 hours of our city and could gig and drive home in the same night. Now we lose money or break even just by the very nature of low-paying club gigs out of town. No pay-to-play though.
Anyway... the point is that you can make a living in music by going all-in, but you leave so many more options open for yourself personally and professionally if you can find a good part-time day gig perhaps and still leave room in your life to play with lots of people and establish yourself in a local scene of some sort - getting 'on the road' occasionally. Also, as mentioned by others, if you ever hope to own a home, buy a car, have good health insurance, etc., it is very likely that money from just gigs (or even teaching) won't ever really cut it, even if you are super frugal.
- you have to find or create your own niche! It won't come to you & you have to be prepared to evolve when the scene changes.
