Somewhere when I was studying composition and arrangement I also started to listen critically to music. That, along with furthering my understanding of compositional structures and harmony, is what I would attribute the most important steps towards becoming proficient in composing.
Learning to play a vast amount of music was also immensely impactful as it brought me closer to the work and allowed me to pick up on a lot of tricks.
I suppose neither of those are really tools per se, but it did provide me with the tools needed later in life.
Thanks Chicago, (btw one of my favorite bands, love the horns and bass player in that group)
Regarding compositional structure are you talking about how to arrange an intro, V1, V2, bridge, chorus, outro, etc?
Did you use an online resource like this?
https://www.musictheoryacademy.com/understanding-music/musical-structures/