When you’re making pictures with people, you need to have practiced your camera well enough that you can change the ISO, Aperture, and Shutter Speed (or Exposure Compensation) without taking your eye from the viewfinder.
Go ahead and practice right now. You should be ‘dry firing’ your camera daily. Take it with you to work and when you take a lunch break, put it to your eye and practice changing all the settings. You need to program your muscles to know exactly where all the settings are the same way you can find your way from your bed to the bathroom without turning on the lights.
When you can work your camera fluently like this, you’ll be able to stay in the moment with your subject much better. All it takes is practice.
Similarly, you need to know what your computer can do when your camera is finished with its work. If you practice with your editing tools, then you’ll be able to look at a picture on your camera and say, “Ok, this part is too dark, and that part is too dark, but I know that when I adjust the white balance and the shadows, everything will look just right.”
I’m not saying you should rely on the computer to fix your photos. I’m saying you should know what your limits are so that while you’re shooting you can relax and know how the picture will look when it’s finished.
I was making headshots yesterday, and as I shot I said to myself, “She’s got dark lines under her eyes, but I know Perfectly Clear will take care of those, and I know that this tone of background will look really good in black and white. But, I need to scoot over to the right so that bright spot isn’t in my background.”
You can make the best portraits you’ve ever done when you know how to use all the tools available to you and practice utilizing them so you know your limits. The great thing is that the more you practice the more your skills will grow and the better your pictures will become. Practice pressing buttons on your camera, and practice clicking on settings on your computer and take note of how much better you become.