Write Something Simple
Each week I've been asking my Patrons to write some music! In my opinion, writing music is the key to loving and learning music your whole life. Of course it's valuable to learn songs, practice technique, learn theory, etc - but writing music is where all the magic happens. Thats when you step into ownership. The feeling of "I made this" is just such a powerful feeling.
This feeling is so powerful, that I think the more you write, the more you want to understand how music works and the more inspired you are to work on all the tedious things. Writing music gives you a context for practice.
You don't have to write music with the intention of being a frontman, a songwriter, a singer, etc. All of those things are more specific than just writing music. If you want to be a bass player, a lead guitarist, a rhythm guitarists - etc - WRITING MUSIC HELPS WITH ALL OF THOSE SKILLS.
In any band, you'll be more valuable if you can write music - even if that just means writing your own parts. Even if you want to play other people's music for the rest of your life, being able to write music will still make you a more flexible player.
If you want to learn to speak a second language, the ultimate goal is to able to say what's on your mind as freely as possible. Writing music is kind of like that, the more you write, the more you'll be able to write the way you want and find the kinds of sounds you want.