Try creating a strong personality first, and then use outward appearance. Once your main idea about your character is decided, start brushing up the outfits and appearances. This is where your character will become an “original character” rather than just a generic idea.
The key component when drawing outward appearances is to create something visually memorable to your audience, such as a color scheme or a motif. For example, if the motif is a butterfly, add butterflies to their clothing and accessories. Even with a character dressed in a typical high school girl uniform, devise something characteristic of their personality, such as a hairstyle or a hand-held item.
A good way to think about key components is, if you were to draw your character as a chibi, this characteristic should still stand out. See the below images for examples of this (these aren’t mine).
Draw movement and poses that go along with the character personality traits as well. For example, a tomboyish girl could wear something that allows for free movement such as pants, and stand in masculine poses. You might also want to study anatomical poses to make sure that their clothes are fitted appropriately.