But I remember Faces

Nature-the world is your source-world of ideas is your source. (Americans would say Special sauce).

Observe the real if you can and distill it down- to a gesture or shape or attitude that conveys the character. It is better if you  can draw from the world or things you've observed and find the truths you want to communicate or stylise than to just think of a shape and try and retrofit a character into it. Why because there's a richness of detail to be had if you take the time to look about the way people look,stand move, the way they talk(same applies to animals) which people may not "know" about will recognise when they see it(more likely they'll recognise somethings missing when its not there). The bits of truth in there will help sell the fantasy, or the character- or the lie as it were.

Characters grow and develop over time, and are gradually refined,- a lot are revisited and reinvented to suit the current time. Remember the character is not just what they look like but how they sound and move as well as what they do and what they say.

Things you might like to ask or try to convey about the character via their appearance.

For a game obviously it is  what is their function in terms of gameplay.

Age?

 Where they are from?

What they do(their profession or job type of clothes, or uniform, tools of trade, expensive showy clothing, sporty)?  

What they have been doing( have they been walking through mud or been rained on- are they damaged or injured or sunburnt?),

What is their  psychological state?(proud, careless or untidy, their social status(rich, poor, revered, destitute),

Their gender?

 What do they believe in or value ?(no possessions, lots of expensive clothes,  a few things but good, practical reliable things etc, lots of high tech things, things made out of natural materials.)