What’s your motivation behind your look?
I build all my mogs around a weapon. Now you go.
Depends on the character, though typically I design around the tabard. I really love tabards.
… Which is why it bugs me that so many of the belts being created in recent expansions DELETE THE FRONT TABARD FLAP! 
i usually just mog tier sets. sometimes i throw some random old pieces together to make my revealing mog. sometimes i base it around a weapon or my mood if im pissed off ill have red enchant on the weapon. no tabards
I tried to get the camo hunter look, not much out there In camo looking gear for hunters
I built this mog around the hairstyle.
Really depends on the Character. I have one character in Warlords, so for right now, his mog is something very matched with that expansion.
This character is in old world/Cata-- So she’s a bit mismatched.
And have one in Outlands that matches the Blood Elf theme from Sunwell.
For Legion and BfA I was a slayer of demons.
With my current look, I feel like a Solar, fighting the forces of evil with a hint of irony. Granted, I’m an excruciatingly weak solar, thanks to havoc being nerfed into the ground. But Solar none the less.
I immerse myself in my character, for example I’m a Wildhammer Dwarf, what would I wear, title I’d use, mount I’d use… everything has to go with the character, even professions.
That’s how I came up with this characters look.
I usually go for sets, but sometimes I will find a piece of gear, whether it be chest, shoulders, or weapon (the main three) that I love and try to build a mog around it. usually i can’t find anything that truly works, but finally, this week, I found one i could make work: the legendary shoulders for plate wearers look badass, so I just had to try to make it work, and thus my current mog was born. I’m still tweaking to try and make it a bit better, but i don’t usually find healm i like, and there’s really no better hands or feet to go with this, so this may be my final rendition of this mog.
usually around the class. if its shaman something fiery maybe.
My Zandalari Venthyr druid has a combo outdoorsy / bat thing going on
I usually try to keep as much not mogged as possible, but then fill in parts that I want to improve according to character class, race theme. For this toon, a bit of kyrian and add gold where kyrian parts don’t impress me.
i build mine around my armor chest pieces. i try to anyways. change things up once a month. used to be once a week but then the artifacts hit and i switched to once a month. got expensive quick. roughly 1k a week per toon. now i just transmog the weapons weekly and maybe the helm if it can fit the theme and isn’t part of the set. i don’t EVER bother with transmogging bracers or capes. a lot of capes are either uninteresting or just clip through the body model/armor.
I never did either until recently. Since we can turn off gloves, mogging bracers has become much more interesting. Here’s an example:
I didn’t like the gloves that went with this set but if you pair bracers with a shirt, you can get this effect:
https://worldofwarcraft.com/en-us/character/us/moon-guard/greta
I transmog based on the character’s RP
i dont bother with bracers because 1. they are tiny. 2. 90% of them are just meh looking. and 3. turning off the far more interesting gloves turns me off to the whole concept. so i think ill pass. didn’t know until now you could turn off gloves. was that recent?
To look like a bamf
Yeah I think right before SL came out? It was sometime in BfA.
Not all of them. Some run the length of your forearm.
Seconded 
I’m a tiny bit disappointed that you didn’t pair a class with your name to wear The Postmaster set and use the Postmaster title.
usually i just see a piece i like or even a barber shop combo and go off that.
had to go off of the wings for this of course. was pretty siked to find out i could basically do kyrian hair, eyes and skin as a void elf.