This type of image you generally focus on eyes, you want catch-lights in the eyes if you can and nice bright mid-tones with even lighting on the face (as light allows).
But back to the portrait type. This type of image you generally focus on eyes, you want catch-lights in the eyes if you can and nice bright mid-tones with even lighting on the face (as light allows). This is preference and will vary on lighting, subject, time of day to name just a few things. I generally shoot with apertures f/1.4-f/2.8 for single subjects. These apertures generally allow me nice smooth skin, with little skin detail and I shoot to overexpose a little bit on the skin and pull it back in Lightroom. If I want a grainy image- then I shoot to underexpose a little and bring it back up (yes I do this on purpose sometimes)- love me some gritty grain (or you can fake it and add grain in LR or PS later).