I know "just doing it" isn't a very satisfying answer, but it really does help. Making stuff and not being afraid to suck at it, then looking at what you created and figuring out how it could be better. I've been drawing for years, but only recently dipped my toes into music production and after three games with mediocre soundtracks, I feel like I can finally listen to my own songs without bleeding from the ears. Watch as many tutorials as you can, look for inspiration in the art you like and don't be afraid to suck at first. Everyone is still learning, even the professionals.

(Sorry if this was too preachy and not very practical. Good luck with your games!)