Personally, to start drawing and writing about new worlds, I first think what kind of characters live there. It helps me think the kind of city or places where they are and how they treat the enviroment on it. Later I think on how this place would look like, taking reference from real places, then adapting it to my characters personallity (inidividually if it's their home, or generally if it's their city); the colors that should be in it, the kind of architecture... etc etc.
to give you an example, I created my oc Lucifer's palace in my comic. It's this character property, and also his home, and also there are a lot of other demons living there. I thought on how a palace of a demon prince would look like, and finally got inspired by the versailles palace but with a total different color scheme: i used green, which is the color that represents the demon, red, black, old wood and light yellow painted wood... I played with the lights too, as he is a very warm person, I decided his palace lighting would be yellow and very warm. idk, take a look if you want
I hope it helps, and if you want to ask something feel free to ask!