What a fun question!! So most of my characters have a specific lack of awareness. This might be interpersonal, situational, or of their own motivations. Not always just one, but definitely lack of awareness. I don't want my characters to know what I am doing while their backs are turned. 

That and (I would suppose that it is a logical consequence) they all seem slightly confused/bemused/curious about the world around them. I think I rely on this trait for a lot of character motivation in the choices they make. 

Another common theme is to pick some metaphorical symbol for them. Rat faced, blade thin, shiny, etc. I think I must use this to keep characters straight in my head. Rodents aren't beetles and gold isn't a birch tree. 

I stay away from apathetic characters. They bore me to tears. 

Huh. Makes me want to create one just to push my own boundaries! Heh.