Three Questions to Create Fashion and Clothing! - Worldbulding 101 

In my fantasy games I like to have horse-focused cultures wear trousers and others wear kilts and sarongs. And if a horse-culture conquers and sedentary culture, that difference becomes a class difference.

If you want to be really organic, you may consider how a cultures resources affect their clothing. (Farming cultures will produce linens and cotton, while ranchers may have wool and leather. ) It's also worth noting that before artificial dyes, certain colors are more expensive than others. Purple was a color associated with royalty due to its cost. A rogue may try to use such colors to impersonate royalty. (This results in laws prohibiting those colors by non royalty. )

And suddenly I've realized that sturdy, jean like clothing with iron charms would be exceptionally common in the current region of my D&D campaign, what with iron warding away the fae and needing to mine said iron en mass to provide it to as many as possible.

My Drows...They mostly wear fish leather, with very occasional spider silk or metal. Everyone would wear slippers, loincloths and adults would wear belts. Belts for men are very wide, from the diaphragm to the lower hip, while belts for the ladies are more narrow, with a maximum of two inches. This reason is, that males do the more dangerous jobs that would require more protection of the soft tissues of the belly. These wide belts can also be used in weathier classes to show of status, decorated with elven hair and nails, centepede shells beeds, gem stones or copper chainmail. Both genders wear their hair as long as possible. On special occasions, spider-silk sashes are worn, made out of washed bandages.

I learned one thing here and it is that women look good in suits.

In my story world, the characters are descended from Japanese people who isolated themselves on a planet that shouldn’t be habitable (but is due to divine intervention), so their garments are based on traditional Japanese clothing. But here’s the twist: they’re descended from *modern* Japanese people, so the clothing is more like “their best guess as to what traditional clothing looked like,” as well as “this makes more sense than how they did it in feudal times.” The end result is that their clothing looks like traditional clothes, but with some modern features like trousers, belts, etc. They wear sandals due to the subtropical weather, but these are a different style from zouri and such. Some people straight-up wear boots. Nobody LARPs as a samurai. The main difference, however, lies with the witches who function as the ruling class. They wear European-style dresses of varying lengths, as well as high-heeled shoes when not traveling. The lower-ranked witches wear outfits somewhat reminiscent of school uniforms. Once these witches leave government service (usually by marrying), they don’t stop wearing this type of clothing, as it’s a marker of their status. Also, non-witches are *never* permitted to dress this way, as magic powers serve useful purposes and you would be misrepresenting yourself as capable of magic. Thus non-witch females double down on the faux-traditional aesthetic. (Men don’t have to worry, as they cannot become magic users in the first place.)

Maybe it is because of my general lack an artist's eye (fashion absolutely is an art), but this has been one of the last aspects I have been developing for my world's culture. Perhaps naturally, I have tried to go for a more practical approach on all levels. Part of it is because of there is no much of a barrier between the nobility and the commoners, so imposing some sort of law saw little backing. Another reason is because of the underlying tenets of the culture, namely that all must be supported, in good and especially in hard times, so no one is allowed to be above getting their hands dirty. Without any class being able to wall themselves off, the more impractical clothing options - i.e. ones that typically require some sort of servant's work in order to have - never really take hold. That said, colors and styles are about as varied as you can reasonably get under such circumstances. Are there subtle differences? Sure (though I will probably never go deeper in detail). Is there a preference for certain types of clothing based on location and local climate? Absolutely. Are there influences from other cultures? Good luck _not_ having them. Mostly because of my laziness, clothing styles from all of the known cultures on Earth can be seen in this world, though they generally have a more modernized look and feel to them. For practicality and thus comfort, clothing is generally revealing, though it differs in two ways. For those who labor in the open, clothing is generally looser so as to allow sufficient proper air and blood circulation. For those behind closed doors, clothing is generally tighter, as the chaos of contained sentient activity makes the risk of accidents ever-present. Both ways usually reveal a fair amount of skin irrespective of gender, but the amount shown typically comes down to personal preference. That said, there are some races where clothing is somewhat discouraged (the ones with more plant-like qualities need as much of themselves exposed for what should be obvious reasons, and what clothing they do wear tends to be the loosest). Their military forces wear the most clothing, but that is mainly due to having to deal with the issues of being military. It gets even more so as they advance technologically (camouflage and protection from the environment are a must for any modern military), but it otherwise stays within the norms of those who work behind closed doors. It is not until they start going into space that their clothing really starts getting overhauled - and this is where my little artistic creativity pretty much disappears, so I cannot really delve into it.