Filmmaking is a tough thing; you need to be thinking on multiple levels simultaneously, and any one mistake can derail the final product. This great video will walk you through 15 such mistakes and how to recognize and avoid them.
Darius Britt has a lot of great videos on the art of filmmaking, but this one is particularly helpful as it gives you some very concrete things to be aware of and avoid; it's definitely worth taking notes while watching. Perhaps the most salient point he made was his aside when discussing clichés: watching more films makes them more readily apparent and more easily avoided. I think this point extends beyond just that specific mistake, however: the best thing I ever did to become a better composer was not some sort of writing exercise. Rather, I listened (and continue to listen) to mounds upon mounds of music until I had internalized the styles and nuances that I wanted to make my own, then I listened to music outside those preferences for more perspective. It's so important as artists to continually experience, analyze, and absorb the art of others, and doing so makes us stronger and more informed with better control of our creative processes.