If you had only one sentence to describe the most important thing you could do as an aspiring musician, what would it be? Short and sweet. Here's mine. Your EAR is much more important than your THEORY; train that first.

Marry someone rich.

Practice.

Never give up. (There's always something else to practice or learn.)

Do it because you enjoy it, not because you want to make money.

I could never, ever do this in one short sentence. Perhaps I could cheat and use cleverly placed punctuation to turn one sentence into a paragraph, but I guarantee any musician worth his/her salt (worth listening to) will have the fundamental wisdoms of music intertwined with their very soul.