Sometimes an image's success lies in how much you (and I'm talking to both shooters and subjects here) commit to it. If you're not a professional model/actor, it may feel weird to have a camera jammed in your face (this alone makes many people uncomfortable) and then be asked to "show me relief," or " look optimistic." If you're behind the camera, you may feel uncomfortable asking for anything other than "smile" (which invariably nets a cheesy, fake grin). But, the magic happens when both sides stop being shy and go all in. This is why I need models/actors for a lot of my work. They don't feel awkward when I say, "Look pensive!" or "Show me dismay." They commit to the looks and emotions I ask for, and they don't feel weird doing it (or if they do, they hide it, I suppose). A particular emotion may or may not work, but it's part of the process as we build to the desired results.
Portraits of people who are not professional models or actors work the same way. When you commit to the emotions and expressions I ask for, we're far more likely to end up with something special. This image of my goddaughter Corey is a case in point. The first couple of shots had no direction and as a result, were simply well-lit but ordinary images of a young lady. My bad for not giving direction, but fixable. Knowing that she's been doing some acting (see this image), I asked her to play a character who is being thoughtful. Without hesitation, she pulled up her hood and became contemplative. It was working, but not quite there, until I turned her to deepen the shadows. Ding!
Maybe you want (or need for specific purposes) something light, with a smile. No worries -- it's the same process. Commit to exhilaration, joy, contentment, rapture, hope . . . . whatever, just let the appropriate emotion take you over -- and that's what the camera will capture.