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Well, an outgoing person would be more likely to wear flashy things or reveal skin whereas someone who's shy or whatever probably wouldn't try to draw too much attention to themselves like that. I guess you need to ask yourself "If I was this character, would I wear that?" And consider the reasons why people wear certain things. Why do you wear what you wear? Are there certain things you wouldn't wear? Same thing for hairstyles and stuff.

You'll also probably want their face and body to match their personality. Faces are usually pretty straightforward in anime when it comes to showing what kind of person they are. You've got your wide-eyed newbie who's full of questions or doesn't catch onto things too quickly, more realistic eyes for plain folks, narrower eyes for sly people or villains... The more narrow, the more cunning, it seems.

I'd say look up pictures of those specific outfits you want. Just search "(country) army" and you'd probably find pictures of soldiers in uniform. If not that, take some inspiration from Gaia; go to TekTek and design an avatar to give yourself an idea of how the uniforms and stuff should look. You could make some changes from there or even leave it the same. It's not like Gaia has exclusive rights to the millions of possible avatar combinations. Just try not to copy things that are unique to Gaia or represent Gaia (there aren't a lot of things like that, though, excluding their holiday mascots and NPCs).