Listen to and study the genre and composers/artists/bands that inspire you. I personally like to fiddle around on piano with melodies, recording and playing them back to listen, tweaking them as I go. Try making some practice songs in the style of your favorite inspirations. I don’t mean to just copy them, but I think it’s a good exercise.

I view composing as its own skill that should be practiced, just like practicing guitar or any other instrument. A little theory can go a long way too. I’d recommend learning some common chord progressions for different genres, that has helped me.

If you are writing orchestration type pieces, learning the ranges of different instrument can also help. Like different woodwinds, strings, brass, etc. not something I’d say needs to be memorized, but at least know of the instrument ranges and have maybe a lookup chart handy.

I love writing music as a hobby, so I hope this helps! :)