When you create a world, you have to think about all of the details. Is it a whole planet or just a land within something that already exists? What characters live there? What is the climate like? And all of these questions will tell what requirements you need to know to decide what clothes, if any, your characters will wear.
Most novels will have some form of humanoid creature because this makes it easier for us, as humans, to form a connection with the characters and care about the story enough to read it. I will not delve into anything about how you can make characters that are not humanoid and make them believable to make your readers care about them because this novel deals with humans.
Once you know something about your climate and character’s form, you need to know if they will require clothes. I am going to go with yes as the answer to this question because it applies to my novel/universe and is the basis for this post. Now that you know they need clothes, are there caste systems that determine anything about the type of clothes they can wear? For this novel, there are no casts but a few types of people hold special positions in society. Where clothes are concerned, it is based more on how much they earn as to how much they can spend on clothes. If their job is higher paying, they can afford finer fabrics. If their position requires them to attend formal functions, then they will own formal attire.
There will be a short story posted here in the future titled “Recycled Couture” that will involve an encounter with a tailor and provide insight into the wardrobes of my society.