Improvisation
Let us never forget that music is a language. It is a form of emotional communication that, like English, can be written or improvised. Composition and improvisation are two sides of the same coin. They cannot be separated. Just like how the paperback novelist is also capable of extemporaneous conversation.
The great Mark Twain once said “It usually takes me more than three weeks to prepare a good impromptu speech.” I suspect he was up all night coming up with that. Improvisers are not in the business of creating something out of nothing. They are in the business of creating some things out of other things. The improviser’s toolbox is slowly filled, but they learn how to use each tool through trial and error.
As a generalist improviser, you’ll have some working knowledge of keys and scales. If you can muddle your way up and down the major scale you’ll be in better shape than most. After that you can develop some more highly specified tools. These tools won’t be applicable in all situations, but when the time comes they’ll be nice to have.
If you’re relatively new to music, don’t go tool shopping just yet. For now, learn songs, write songs, and enjoy songs. You’ll be picking up a lot of tools via osmosis. Explore each and every musical idea that comes to mind. If you hear a note in your head then find it on your instrument and learn what it is called. Bite sized theory early on in your development will prepare you to make elaborate meals in the future.
When you’re ready, find a friend or a Youtube jam track and try to make something up on the fly. Or just play a bunch of random notes. Pay attention to what you’re doing and take mental notes about what is working and what isn’t. After that, try to learn why this things works and that thing doesn’t. Take risks.
Marc Maron said "I don't really believe in preparing. In my mind if I get up here and pull this off then I'm a genius. And if I don't pull it off? Eh, I didn't prepare." Maron was no amateur when he said this in his 2013 comedy special Thinky Pain. No, Maron had already honed his craft for decades and he mastered the ins and outs of comedy. Now he has the freedom to walk out on stage with only a vague idea of what he’s going to say. The more you work at music the more it will reward you and you may one day find yourself in a similar position.