I would shoot at nothing below f16, f22 is even better..mount a flash remotely on a tripod and get one of those remote triggers so you don't need a cable to connect camera to light. By shooting stopped down to f22 and with a high quality ettl flash you can get Gary Lang type quality shots with a little practice and patience.
I would also try to focus on the eyes. Other things being out of focus can be a little more forgiving, but out of focus eyes are unsettling.
If your subject doesnt move, then mount both flash and camera to tripods and use an image stacking program and take multiple shots only varying the focal point. Merge all the photos with an image stacking program, and voila you have instant depth of field.
I f none of that is possible, then move back from the subject and crop your photo accordingly.