What is it about people that makes them individuals? Clothes? Hairstyle? Sure. I always find it amazing knowing that there had to be thousands, if not more, of some common article of clothing, and yet you almost never see two people wearing the same thing, not even matching shoes or jeans. But it takes more than trappings to make an individual. Mannerisms can be just as varied as a person's choice of clothing.
If by some chance you could dress all your friends in identical clothing and fix their hair the same, how would you tell them apart? Look closely. Sure their face is recognizable, but you're not looking at their face. What are the clues?
Joe always has his hands in his pockets. Bill never stands with his weight evenly distributed on his feet - always leaning, say, to the left. George can't seem to keep his heels on the ground. John is always running his fingers through his hair, or pulling on his beard if he has one.
Do you get where I'm going?
Marie is always tucking her hair behind her ears, whether it needs it or not. Linda really needs pockets - she can't figure out what to do with her hands so they are always fluttering around. Jennifer walks like a cowhand, swinging her shoulders instead of her hips. Karen is always seeking the perfect adjustment to her clothing and never seems to be able to find it.
There's the person who can never look another person in the eyes. People who walk in quick short steps, or long easy strides, or silent animalistic steps. People who stand with their chin high, seeming to look down their nose at everyone, intentionally or otherwise.
The choices are nearly infinite and extend far beyond body movements. The way a person expresses themselves apply too. There's the person who can't seem to say a complete sentence without sighing. The person who struggles very hard to be indifferent about everything with a shrug at every turn. The person who seems to smile all the time, making light though taking whatever seriously enough. The person who is habitually serious, and possibly very literal, and maybe can't take even a simple joke, either being offended or completely missing the point.
Do you know people like these?
You've heard the expression, I'm sure, 'cookie cutter character'. Cookie cutter characters happen when all your characters express themselves in the same way. It doesn't matter how different they act, dress, or what they say. If all of your characters walk (using the same word) or they can't make eye contact or they are always giggling - always - they become cookie cutter characters. It becomes difficult to tell the difference between one and the other, regardless of dialogue tags and the story thread.
Don't be afraid to give your characters their very own personality by allowing them to express themselves in their very own way.