I find this quite tricky actually. 
When I first started I went for really bright colours, crazy hair styles, face markings (for no reason at all) and weird outfits (flip flops and camo shorts!? lol!). Then I stepped back and realised that wasn't really the feel I was going for at all. I wanted them to look a bit more serious to reflect the actual story.
Old: Triangle nose and weird feet. What was I thinking!?
New: Less is better I think (I hope!? Sometimes I worry I'm making them boring.
). Lost the face stripes, crazy hair style and he has normal feet under those boots now. The clothes/armour need to be light weight. Poncho because a traditional cape would get in the way. Leggings because he's a stretchy little dude. Boots because they walk A LOT, and usually through woodland and muddy places (again - what was I thinking with the flip flops).
I'm trying to give the world a medieval vibe, so clothes, hair styles and weapons etc. will be along those lines - but as it's not set in our world I have a bit of a leeway I suppose. 
Practicality wise - I had to rethink some outfits. For some reason (in an earlier attempt) I had most of the females in skimpy or pretty outfits, which might have looked nice or whatever - but could they really spend a week in the woods in those clothes!? And did they actually reflect the characters wearing them (no was the answer).
Old:
New:
Old: Boobies about to jump out, and some sort of crazy hair going on.
New: Still (hopefully) sexy & intimidating (I mostly do that with her body language now), but the boobs are at bay, new hair style and she'll be a bit warmer at night. I kept the green as (unlike original Gen) she does want to be camouflaged sometimes. No shoes as the Aamami do have paws for feet and need them out for speed (they are a type of Hare).
I'd say the ladies designs are the trickiest actually because they are strong characters and I want them to be taken seriously.