You must have orchestral pieces that you really like? Maybe even, like, film scores or musical theater scores? When I first got started soooooo long ago, I would spend hours listening, replaying, transcribing, and writing everything that I heard. And holy hell, I definitely got better because I was engaging my brain in piecing everything together. Copying note-for-note is alright (as long as you're listening alongside it), but transcribing it arguably even better. And, bonus, you get to practice transcription too!
But yeah, basically, don't be so beholden to the original work, is my biggest advice. There's a reason that every collegiate composition course in the world has you take a very, very short piano miniature and orchestrate it. I remember my class took Ligeti's Musica ricercata, II., and orchestrated it. Super short, and literally only three notes. It was hard. But with practice—and creativity—it all comes together.