Music composition tips? Asking as a Vocal Synth user

So, I've been a fan of Vocaloid for over a decade now, but I've only really messed with it and similar programs (UTAU, Synth V) since 2017. Now, I took a huge break, but! As of this year I bought Synth V properly and Kasane Teto :) So far been having a lot of fun with it, but I am. A bit slow when it comes to producing music. It's definitely not my strong point, and for some reason the stuff I made in middle school sounds better than the things I made recently; a bit irksome imo. 

Either way, since I'm looking forward to using Teto more and more for songs, I wanted to see if anyone had tips or tricks for music production! This can be anything, from good software you've found, or maybe you know things about vocal synth stuff that is a good tip! Y'know, stuff like that.

(Salutes) Hope to post my music here sometime, but for now this will do.