Practice and improvement, that's what it need.
Well, everything needs improvement, your walk cycles, your backgrounds, your characters, the audio... nothing practice and study other animations as well can't solve. Just decide what you're more interested now, for example, perspective, or maybe ways to tell story not always "with the camera on the front" like it was a theater, by the way, don't get too upset about it, I'm almost sure that most animators begin making everything very flat, by now I recommend you try to repeat the scene of any movie or animation you like, it may give you some ideas beyond practice, really. You could even adapt some sitcom episode to your series, who knows?