Your saturation is pretty decent. However some look a bit overexposed, especially in the light-skinned faces. Try bracketing, which is taking a few photos of the same pose, one with your light meter reading at 0, one a stop below, and one a stop above. It will help you find where it looks best. You should also be using selective focus points if you are using autofocus on your camera. Forgive me if this is a little advanced, I do need to know if you’re using a DSLR for that to make sense. When you use selective focus points, focus on their face, especially their eyes. This will also help your light meter read correctly for their skin.
Here are some of my own examples of filling the frame vs. using negative space to your advantage.
Negative space, with subject off-center: http://www.flickr.com/photos/roxanne_elise_photography/8225598305/in/photostream
Negative space, not too much background, but enough to help create the setting: http://www.flickr.com/photos/roxanne_elise_photography/8111653230/in/photostream
Filling the frame: http://www.flickr.com/photos/roxanne_elise_photography/8005388698/in/photostream (Creates more “dynamic tension” which pulls your eyes to different ends of the image- this is more useful in action shots)
Almost filling the frame: http://www.flickr.com/photos/roxanne_elise_photography/7928198598/in/photostream
But remember, just because I shot these particular images this way, doesn’t mean it is the only “right” way to do it. Would my first image look ok cropped in closer like a headshot? Yeah probably. Would my basketball guy look fine with more background showing? Maybe.