I find myself giving the same advice to different students each semester at Concordia, where I teach applied composition. Some of these tips echo a great article I read recently by Adam Benjamin. His target audience is jazz writers, but it's a good read for any composer, regardless of genre.
Another excellent resource is the Portfolio Composer Podcast, where my friend Garrett interviews professional composers about their careers. Tell him I sent you!
Here are some things I tell my applied composition students:
WRITE AS MUCH MUSIC AS YOU POSSIBLY CAN. It won't all be great, that's okay. Just write it. Think of the pieces you compose the way a baseball player approaches at-bats. Sometimes you get a hit, sometimes you strike out, once in a while you'll hit a home run. The important thing is to get up and take your swings every day.
DON'T REVISE A FINISHED PIECE OVER AND OVER. Get to the final barline, clean it up, and get it performed. Maybe revise once. Then onto the next one. The way you get better is by making the next piece better.
WRITE MUSIC FOR YOUR FRIENDS. Find someone you know who plays or sings really well and compose something specifically for them. Show them drafts in progress and get their feedback about what works and what doesn’t. The relationships you build now can have big payoffs down the road.
RECORD EVERYTHING. Get a portable recorder if you don’t have one already. You’ll learn more in one minute of hearing your music played by humans than you will in hours of composition lessons. Anytime someone performs your music, record it. Record rehearsals too.
PLAY PIANO AND SING. Knowing other instruments is great, but these two are the most important. Every instrument is at least a little bit like the human voice, and if you plan to write more than one note at a time, you’ll be glad you can find your way around the keyboard.
DEVELOP YOUR EAR. If you didn’t ace your ear training classes, get back to work. If you have strong ears already, transcribe super hard stuff until you get even better. Composers should always have the best ears in the room. If you can’t identify intervals and chords when you hear them, how can we trust that you mean the notes you’re putting down?
"IF IT SOUNDS GOOD, IT IS GOOD." Don't ignore this obvious advice from Duke Ellington. Write music that sounds good.
WRITE BY HAND, OR DON'T. There's no right or wrong answer here. Staff paper, computer, whatever. Just write. Of course you’ll need notation software eventually to finish the piece, but for the initial composing stages, do what works for you. I know some composers who write entire pieces by hand, and then engrave all at once. My personal preference is to compose little sections at the piano, then get them right into the computer, editing on the fly.
WRITE A "BAD ENDING." If you’re having trouble sticking the landing, write a placeholder ending that is purposefully bad. Get to the final barline. Wait a day, then rework the bad ending into something better.
WRITER'S BLOCK? Rearrange the furniture in your composing space. Seriously. Put your desk on the other side of the room. Then try again.
WRITER'S BLOCK? Get outside. Run around, mow the lawn, walk the dog. Then try again.
WRITER'S BLOCK? Power through. Get something down, even if you hate it. You might like it tomorrow. Even if you don’t, you’ve changed your problem from “I’ve got nothing” to “I need to improve this.” It’s a more manageable situation.
LISTEN TO EVERYTHING. Soak up all the music you can. Find good stuff in different styles and genres, and wear it out. The music that seeps into you over time, by osmosis, becomes your vocabulary. It’s the most important thing that informs your own writing.
If you know any young (or not-so-young) composers, or composition teachers, feel free to share this with them! I’d love to hear from anyone who has other good tips.