This is an exciting question, and you are so lovely to even say anything about this~

When dressing someone at all, I keep tons of reference around.  I’m not a huge fan of mix and match pieces and parts from canon  for the most part, because it can feel a little flat (more on that at the end) though I do like that it gives the illusion of a wardrobe, since not everyone wears the same thing the same way all the time, you know?  That was fun to do with the Johnny fandom stuff, though that turned out to be a whole other kettle of fish from what you’re asking about since it was an AU and I ended up designing all the clothes and styles myself.  

It’s fun in Doctor Who to do that, though, because I love thinking about the TARDIS wardrobe room.  

ANYWAY, I’ll use Garak for a lot of this, since I’ve been working with him lately.

Dressing people is something that can be done in and out of character just as much as writing how they act.  

The backbone of this stuff is always research of some kind.  So references are a big thing.  I’ve got to see what kind of necklines are on Garak, or what colors, or what shapes and cuts he’s in.  And actually, it’s good to see how his clothing compares to other Cardassians so I can see what’s different about him, or what sets him apart.

Garak has been difficult because he’s alien.  You’d think this would be freeing, but it’s actually a little intimidating.  Something I’ve been doing in this case actually is tracking down behind the scenes stuff and design ideas for the whole of Deep Space Nine.  I found several people talking about the architecture of DS9/Terok Nor and they said something they did to make it ~Cardassian~ was to make the basic element of composition a hexagonal shape, rather than a circle.  So there is more harmony and aesthetic enjoyment for Cardassians in the pointed shapes of the station.  And you can see this hexagon thing going on on a few of Garak’s clothes.  Even the notches in his necklines (front and back) give his neckline a total of six ‘sides’. Not equal, but it’s maybe like humans enjoying ovals as well as circles.  

Garak also shows up in greens quite often, which seems to compliment his skin and scales well. Though, we also see him in some very bright colors (red, yellow) while few other Cardassians are clad in anything but desaturated colors.   As lovely as I think he’d look, I try to keep him out of black and steel-y sort of colors since it looks so much like the armor Dukat and the others wear.   

Garak also seems to be very fond of vertical lines.  Slimming? Trying to give himself some more height? He’s a tailor, so he’d know about this kind of stuff.  (Which makes him really intimidating to clothe, because you’re essentially asserting that what he’s wearing is a Good Idea by virtue of putting him in it.)

That’s part of considering the character, too.  What do they do, what are they comfortable in?   Garak is always cold on DS9, so he’s always long sleeves.   

The Doctor (Doctor Who now, not DS9), similarly, is always a kind of gentleman, even if he’s maybe a parody of one, and thus seeing his bare arms always feels a little like we’re seeing something we shouldn’t.   Not that I redress the Doctor very often, but he sprang to mind. 

When people are not Garak, I’ve been lucky that they’re human, but a lot of the same stuff applies.   Find a sort of peer group to compare to and use that to an advantage. That’s really useful with Doctor Who.  Compare Jamie to other highlanders of his time to get an idea of what he might naturally consider a Good Idea, fashion-wise.  Compare him colors-wise to The Doctor and other companions.  Polly was very 60’s, but her 60’s was a little different than Susan’s.  

While I’ve been doing all this DD9 stuff, even, I’ve been trying to consider environments and histories in dressing Julian and Garak.  Julian’s wardrobe is all simple pieces and things he got for free from events at school and weird giveaways and thus it’s all kind of ill-fitting and super casual. 

DD9 Garak I had this weird place to consider where I was trying to hold onto his alien-fashion-ness somehow, so I settled on ‘asymmetry’ and kept a little of the hexagonal DS9 in there.  So his collars and hems are generally off-center somehow, and everything he wears is structured and tailored.  He’s in darker, desaturated, rich and elegant colors, and Julian’s colors are usually kind of garish and unrefined looking.  I dress them, in many cases, as a balance against each other.  Since they’re illustrations, they have to be (and can be!) pushed a little more than they would if they were on screen.

The trick with all of this is not get obsessed with one particular feature or they start to feel flat, just like writing a character with obsessive harping on a particular line/trait.  I had once used the example of ‘If you have a character who canonically is always smacking into doors, it is not enough to make him feel real to just constantly write him smacking into doors.  You’ll do far better to think about WHY he’s hitting those doors, because then you get deeper, and the character really lives in why he hits the doors, and why he only wears long sleeves and where and how he feels comfortable, not just that he DOES. 

I hope that answers your question!  Hope all the Garak references don’t make this useless, I’m just literally doing a fashion show commission thing starring him, and so he’s particularly relevant to me at this point!