Proper lighting in portraits can be challenging. Flashes often are insufficient or over powering. If you have a standard height white ceiling, then bouncing your flash of the ceiling, tilting you flash about 45 degrees above level. Getting your flash off your camera with a flash cord designed for your brand of camera can improve you flash fill too.
It’s likely you are doing things like this already, and maybe you even use a soft box and umbrellas. But to really make that headshot pop, ask your model to hold a piece of foam core or white matte board angled to bounce the light to the lower part of their face and of course outside of the view of your shot.
The light will fill in your subject and even up the light very nicely. Chances are you already have some foam core or matte board just laying around.
What an improvement this little reflector will give you!