Make yourself a little exposure and focus target.
Get a piece of white foamboard, maybe 5x8 inches, but the size is not too important. Divide it into thirds for area, and cover one third with the blackest black tape that you can find. One third you cover with gray tape that is about 18% gray. Then the last third, you leave as pure white.
Now you can use it for two things. First, exposure. If you shoot a photo, ideally you should get three spikes on the histogram. The black piece should yield a spike at the far left side of the histogram. The gray piece should yield a spike in the center. Then the white piece should yield a spike on the far right side. If your exposure is all wrong, you will see a weirdly offset histogram.
Then focus. The camera should be able to autofocus on the contrasting lines of the thirds of the target. A gray card might give it some trouble, but black-gray-white ought to work good.
Get your model to hold the target near the eyes, if that is the primary interest.
---Bob Gross---