>>96891451I base character design off the concept and personality. This helps keep the design from having too many elements on it for no actual reason, and lets me focus on making the design suggest the character rather than trying to retroactively explain it (messy!).
Let's say my core concept is a simple "arrogant, classy CIA agent". The design has to make you think of all of those things. So in my default design, I'd focus on the suit. Maybe leave a suit jacket open with the dress shirt underneath to suggest a kind of formal-casual cockyness.
To make sure people think "secret agent" instead of "secretary" or "businessman", I'd add some cool mirror shades on top to give that MIB feel. Maybe put a walkie-talkie or an earpiece or something on there.
If I want to make them look like they're a fighter, I roll up their sleeves, but keep the gloves on. Classiness.
And when I draw their "default" stance, I'd go for something with the chest out and the chin up.
If he's supposed to be a SLACKER, I'd untuck the shirt and make him slouch. Maybe add some stubble.
That kind of thing, along with colour, is important. Lots of bright colours can make people think a character is brighter and goofier, or more fiery in the case of reds/yellows/oranges. Blue and some deep purples feel colder.
If there's any important backstory elements, I'd try to hint to them on the design, like scars and stuff.