Use a purposeful setting
Choose a location or prop that contributes to the portrait's question. Remove objects that compete without adding meaning. Ask the subject how they relate to the setting instead of assigning them a fictional story.
Find a workable gesture
Give simple actions rather than rigid instructions: turn toward the light, rest a hand, look at a familiar object. Review how these actions change posture and expression while respecting the subject's comfort.
Edit for character
Compare images for the quality of attention they invite. A technically imperfect frame can be more revealing than an immaculate but distant one. Select with the subject when the intended use makes that appropriate.