My silly little exercise is when I'm out and about doing things, I ask myself what a certain character would be like doing whatever it is I'm doing. What posture do they carry, how do they walk, what would they think of the people around me or the general surroundings? What would they be trying to accomplish/ what are they looking for? So on, so forth. If you do something like that, it becomes a lot more natural later to write from their perspective and highlight their quirks and actions.