You mention your portraits turning a bit too "desaturated" but whats happening is that there is no color variation within your tones
If the lights are slightly warm, make the shadows slightly cold(or vice versa)
skin that turns from dark to light you cant simply blend the two tones together, there must be a 3rd tone in between them value wise, but more saturated.
lastly, avoid making the backgroun the same hue as the skin tone.
you are on the right track overall tho! keep working hard.
if you want some good reads. James gurneys Color and Light is a fantastic place to start.