If you have been at this game long enough you have come up with methods for getting subjects to give you something more for the camera. I’d say “relax” but it’s not always about them relaxing, depending upon the type of photo you need a little tension can often be helpful.
I am not in the habit of telling jokes during a session, if it’s warranted I’ll act a bit silly to try and draw them out. But it’s not uncommon to get an executive who only has one look, they’ve used it for years, and that’s all they’ll give you or you have a subject who is not used to being photographed. In both cases it’s helpful to have a few actions up your sleeve to refresh the pose.
The two images above were not consecutive but they come out of the same action, look down and when I count to three look up. Simple enough, it forces the subject to pose anew and it can often get them out of a tensed look or a frozen smile. If their eyes tend toward deer-in-the-headlights it’ll give you a few moments of reprieve before it sets back in and similarly if they are an active blinker.
In the case above, the subject was great but a bit reserved. Look down/look up helped get a moment of connection beyond the standard business look.