My composition was a classical orchestral, and was edexcel so its obviously very different so some things I say might not apply, but the most important thing for me was to really listen to what your teachers say, they are the ones marking your piece so something they suggest will probably be marked higher by them. Another one is dont be afraid to completely restart your piece, ik someone in my class wrote 4 different pieces for 1 submission because for them it was easier to competely restart from the beginning based on something they liked rather than try and change somethign they didnt like. Just get it out of the way too, I finished my composition in the first 8 weeks, so I had so much spare time to really just do whatever I wanted, and it might seem boring but its much better to have way more free tiem than to be like one of my friends who hardly finished before the deadline