I am not Jesus
but I will offer some advice.
If you shoot off hand, keep the shutter speed near 1/125 or faster, if possible (the rule if thumb is 1/85). Choose the lowest ISO which would allow to shoot without noticeable motion blur (check the screen). Keep the camera steady, stop breathing and shoot (then resume breathing). One hand holds the camera, the other supports the lens. Use the center AF on one of the eyes and recompose. Try apertures from wide open, to f/4. All this depends on the background.
If you have a monopod, use it.
Framing is critical. Try half body, shoulders and face, etc. Avoid harsh light but also avoid situations in which the face is too dark compared to the rest. Again, watch the background. Bright (but not too bright) and colorful background, well blurred, works best, IMO. The background is as important as the main subject but since your model would not change, the background is even more important.
Keep the white balance to auto and take a few shots of gray things under the same lighting. You can use them later for WB correction. Shoot RAW, of course.