The African-American fellow has the best lighting on the clothing--we can see the color and detail in his jacket nicely, but the main light is so high that his eyes are in shadow, and look what is often called "dead"...no eye sparkle at all, zero catchlight. His nose and cheek also have very hot specular highlights that are distracting--the flash needs more diffusion, so the highlight is more diffuse, and less specular. His placement in the frame is off-balance; his shadow takes up some of the left side, the gutter, and his camera-right shoulder takes up a huge amount of space, due to the way he is angled. You've got the body positioned oddly, and had to center the eyes in the frame, and because of that, it gives the portrait a "gutter" that runs top to bottom,left side.
The Asian woman looks the most under-exposed of all. Her clothing appears very dark and featureless, but maybe you could lighten the image up in post, and get some more detail in her jacket. She appear petite, and so her square to the camera shoulder posture doesn't make her look overly wide, but instead makes her look wooden, dull, boring. Shoulder-square is a dull kind of body posture in a photo. It seems that she has ZERO reflection on her skin, which makes me think like many Asian women, she uses a high-quality translucent or mineral makeup powder as the finish on top of her makeup, which is an excellent way to approach photographic makeup.
Guy with striped shirt. First off, help him tie his necktie knot better. If you've ever worn a tie every day to work, and I have, you'd know he looks like he never wears a tie and doesn't know how to either properly tie, or center the neckwear. The knot's too big on such a skinny tie, and it's tied poorly. And there's one inch of shirt on the left side, and 3 inches on the right side. This looks sloppy, and is YOUR job as a photographer to correct these kinds of basics before even shooting a single frame. Correcting wardrobe flaws like flyaway hair, necklaces with the clasp in view, rings with stones downward, lint or hairs on lapels and jacket shoulders, making sure that all that stuff is checked out, and corrected if needed, will show your clients that YOU are on top of things, and it makes the pictures far,far better. He needs to tighten up the jawline to get rid of that under-chin fat. Look up Peter Hurley, It's All About The Jaw and watch the video. Lighting? Okay. Posing? Square shoulders, dull.
Woman in black, last photo. Camera is too low, and shows us all an up-the-nostrils angle of view--unflattering. Lighting is awfully harsh, and shows a lot of skin texture. She is posed weirdly, and appears to be leaning BACK, and away from the lens, while giving a pretty good fake,practiced smile. She could look better with a more forward-leaning pose. Leaning back and away is negative at the subliminal level.
If you want to get better at posing people, you need some instruction. And it can be hard to find. Making people look really GOOD takes a lot of knowledge, and skill, and practice. No offense is intended by anything I wrote above, but this looks like "speedlight work". It's very,very,very difficult to do the best-quality portraiture without modeling lights. The ****exact*** placement of shadows and highlights is all just a guess when working with speedlights and an umbrella. There's also a somewhat "gloomy" look to the light modifier being used here...it's...not...quite..optimal for your flash unit. I spent a lot of time typing this. I hope you can take away something good from my efforts at giving this detailed C&C on these.