Contrary to what most people think, most working musicians do not tour the world performing before throngs of screaming fans or signing autographs at records stores. For every rock star, there are probably thousands of teachers, studio players and live giggers, sound guys and instrument techs. Though you and your amazing band will probably not be rocking Tokyo anytime soon, you can make a living playing music, and trust me, it sure beats a day job!
Step one is to learn the fundamentals. This doesn't mean you just learn how to shred and leave it at that, or play hours of slap bass until the local authorities give up and call in the military to get you to stop. You have to be well-rounded, otherwise you will not be in demand. There are a million and one noodlers, and the truth is, no one really wants to hear them. To work in music, it will be most helpful if you can play fast as well as slow, loud as well as quiet, and to know when to lay down a groove or step up for that jaw-dropping solo.
Study theory, take some private lessons, "wood shed" a bit, and eventually you will become an experienced and confident player. If you have not done so already, explore outside of your #1 choice for listening. The best choice if you're at the "I like punk! " or "I like metal! " stage is to listen to the styles that provided the foundation for the music you love. Believe it or not, a lot of modern music came from the Blues, Country, Classical, Jazz, African American and Native African music, Island music and so on. It's a melting pot! If you're into Metallica and Slayer, pick up a Black Sabbath album. If you've already done that, try some BB King on for size, or Eric Clapton. You'd be amazed how much history your music has - whatever your music is. The more you know about the foundations of music, the better off you will be. The best part is, you will find out about a whole bunch of artists you probably didn't even know about before.
The next step is to expand your marketability. Expanding your instrument base is a good way to do this. Do you play guitar? Well how about learning bass, too? Same goes for bassists - learn guitar! If you play two - or three or four or fifteen - instruments, you are that much more in demand than you were before. You may love sitting in your living room busting out the deep blues on your strat, but if someone is willing to pay you $100 to sit in on stand up bass tonight, what's wrong with that? The answer is nothing at all! The best thing about doing this is that when you go to play in a band setting, you will have a better understanding of the other players and their roles within the band. If you're the lead guitarist by trade, you'll learn to listen closely to the bass player and feed off of the bass line. Doing so makes an unbelievable difference in your sound. If you play keys, learning drums will make you more percussive and dynamic. No matter what your passion, the better you understand the big picture, the better you will play.
Finally, be professional. Remember, this is your job. As with any job, you are expected to show up on time and do what is expected of you when you are hired. If you're playing a wedding reception, leave the Slayer t-shirt on the hanger. Unless you're doing Kerry King's wedding, of course. Weddings, Bar Mitzvahs, hey, these may not be the places you always dreamed of playing, but have you ever seen the bill for a shindig like that?!
Jobs as a musician include, but are not limited to; studio sessions, live gigs (of course!), teaching - (this can be a very lucrative job, and you never stop learning yourself), director - (how about leading a band?), producer, technician - (someone's got to tune those guitars!) The sky is the limit, but the trick is to be open-minded. You and your black metal band probably won't earn a lot with battle axes and chain mail alone, but if you do that on the weekends, teach kids and maybe do a wedding or two during the week, you may never have to cut your hair or wear a suit! The best thing about being a professional is, you never stop playing, so you never stop getting better. If you think you shred now, wait until you're going 6 days a week.
Good luck my friends.