I've been giving this writing advice to a lot of my friends lately so I'll do a mumbling post about it here.
You gotta play dolls with your characters.
Slap them in AUs, make silly fanfiction, make "what if?" senarios. You gotta recreate the feeling of taking your toys out as a kid and improv-ing a story on the spot. You'll get a sense of what makes them who they are outside of their main storyline.
Take a piece of yourself, expand and explore upon it. Create characters and storylines that are love letters to those you've cared most about. Take that little ball of hate and/or despair and give yourself a little therapy lesson.
Be bored! Be frustrated! Be unsatisfied! "Someone should make a story about ___" YOU should make that story! If you aren't satisfied with the media you see, make for yourself the story you DO want to see! Don't worry about how others will view it. For right now, for right at the beginning, the only way you're gonna make progress is if you're having a bit of fun.