Concentrating on specific clothing styles is time consuming; we’re after a general sense of style. For example, the existence of buttons as a fastener, rather than as decoration. We take those for granted, but they didn’t exist until the 1300s. What do people do without them? They wear looser, baggier clothing that may be tightened with a string of some kind; the clothes may just be wrapped around them (like a toga). This can impact culture; when buttons were introduced, so was tighter clothing, which could leave less to the imagination; resistance to the button could therefore happen because it causes a shift in culture, one that challenges ideas on modesty. Decide if buttons exist in this region or sovereign power and whether tight clothing is possible, and whether the existence of buttons is new or taken for granted (just like tighter clothing may be).
This is just one of countless examples, but it illustrates how the technological elements of our world impact and change culture. If we’re thinking that only a fairly simple society may not have buttons as fasteners (decorative buttons are much older, to 5000 BC), such as a nomadic one, the Roman Empire didn’t have them either, and yet they had aqueducts, dams, and ballistae. This surprising incongruity is real but if we do such things ourselves in a story, the audience might think we’re making a mistake, so it may behoove us to meet expectations. Maybe we shouldn’t have our star fighters not knowing what a button is.
Clothing can be used to indicate status, gender, rank, and social class. Plainer clothes suggest something lower while more adornment is for finer folk. Tunics in ancient Rome were adorned with colored bands, where the width, number, and color of these indicated standing. We can make up our own interpretations, such as wide and golden meaning better, and narrow, fewer, and more mundane colors meaning lesser. Decorations can be around the hem, neck, or wrists, but the front or back design was less common long ago on Earth, unlike today. Finer fabrics also suggest wealth while coarser is for the poor. Richer colors, or even clean and bright ones, can also indicate higher status. Consider how important status is to the culture and invent such expectations for cultures where status matters the most.
But even in cultures where visual indications of status are less important (possibly due to being a melting pot), situations will still call for traditionally finer or more mundane clothes (church, a job interview, being on vacation). Those with the highest status might still indicate it with designer clothes, even if just wearing a skimpy bathing suit.
This means that we can still decide what constitutes higher fashion and a reason for this. Tailored clothing makes one look better, so this is an easy one. On Earth, even those of us who can’t afford Louis Vuitton or Prada have heard of them, so we just invent a few names on our fictitious world, and we’re done. We need only reveal its value in a quick line:
She strode in with a diaphanous Olliana gown flowing about her, the price of which would’ve fed a city block for a year. (italics)
Clothing can reflect what is important to the society, groups, or individuals. If hard work is admirable, then sturdy, dependable, simple, rustic, coarse, and unadorned clothing may dominate. Or is clothing ostentatious with embroidery, jewels, and richer fabric like silks? This might appeal to high society that want to wear the latest fashion, sacrificing comfort and durability for appearance.
Modesty is a major cultural element that manifests in clothing, not only in adornment, but how much of the body is visible. Are women allowed to show cleavage (but not “side boob”)? How far up their legs can hemlines rest? Above the ankles, above the knees, mid-thigh, or can they wear a thong in public? Do bras exist and are they expected to hide any appearance of a nipple, or do they push breasts up, as we often see in medieval period films? Can the belly be shown? The shoulders? We should consider how sexually open or repressed the culture is; religions can and will impact this.
One option is to decide that culture is static, regarding clothes or anything else, and therefore newer, more revealing styles (possibly originating from another culture) can cause one culture to harshly judge another as promiscuous and not caring about family values. We can see how values lead to cultural ideas that manifest in clothing, in this case, and an observation of another culture’s clothing leads to a (contemptuous) judgment about what they value. This is what culture is for with world building.
Do men wear pants? What about women? In the United States, a woman wearing pants was once considered to be acting like a man, and this was frowned upon. It brought accusations of not acting like a lady, not knowing one’s place, and being an unacceptable companion. We can do the same thing in our setting, regardless of what men’s fashion a woman has chosen to adopt. Imagine the contempt heaped upon a man if he chose to wear dresses. In our designed culture, we can decide on norms for gender and then have characters violate it for reasons that are often practical; pants are more utilitarian compared to dresses, for example. A rebel will oppose norms just to do so, but such a character typically has attitudes that cause this.
Our cultural vision should influence these decisions.
The economy can also impact clothing due to choices or lack thereof. Those who cannot make more sophisticated clothing must do without or barter/buy them. An isolated culture may have this problem, but so can poorer individuals in societies with significant trade. This can result in limited options and predictable styles for lower classes, ones that become part of culture so that someone who comes into significant money and upgrades their wardrobe might be seen as putting on airs. Note the value judgment.
Footwear can also be cultural. In warm climates, sandals or even bare feet might predominate, while fur-lined, leather boots may in cold locations. A traditional style can exist for either so that those who go against this are judged. While climate affects the choice of how much covering is typical (a universal consideration), the exact styles are not important to our audience and we have leeway to decide what’s expected and what’s a deviation and what the value judgment is.