It's good to take your time when it comes to character design. Do your best to not always go with the first design you create. Here are some things to keep in mind when creating your characters:
Setting. This includes time period and location. You may have two characters from and dark ages/medieval time period but one is a monarch that lives in a summer villa most of the year and the other is a peasant dock worker that lives always by the ocean. Location will especially inform the type of clothes your character will wear. If your character lives somewhere hot, it'd be weird if they were always dressed in summer clothes. Occupation can also fall under this umbrella and does a lot to inform the audience of what the character does and what's expected of them
Age. The young and the old don't dress the same and nor do they look the same. While there may be overlap in the attire, for the most part and old man wearing overalls is going to be different from a young child doing the same. Teenagers and young adults often follow trends in fashion and the media they consumes also influences them. There's more to an elderly person then just a few wrinkles around the eyes; don't be afraid to add lines to the face, liver spots, balding and poor posture. Old people are aged. A lot of creators try not to show it despite how jarring it may be to have an 85 year old with the complexion of someone in their late 20s.
Race/Place of origin. when it comes to stories; we storytellers can make our settings as fantastical and odd as we want. At least when comes to human characters, it's not easy to stray away from the features we deem as human. And one of the most important features is skin tone (and stereotypical physical features). To say a stereotypical Asian person has slanted, dark colored eyes, dark hair, and yellow/golden toned skin is to sate the obvious. You can follow the conventions of a race or you can stray away from those conventions in subtle ways. Maybe you have a race of dark skinned people, bu instead of having dark hair, most all of them have light blond hair. In a general sense, it's good to keep these conventions in mind, but you don't have to follow them.
There's so much that can go into a character that can be told visually or through dialogue. This is just a small blurb that doesn't really go into the backstory part of character design. There are plenty of more visual tips out there including silhouette, color palette, and style. That's all I have right now.