Candid snaps are tough, here are a few things, maybe.
Either crop the frame to horizontal or add more tilt. Try to get some emotion. One thing I've noticed over the years is that the best expressions often happen right after the photo-victim gets snapped. Either shock, or moderately ticked, or suprised, or a laugh...so shoot one, keep the camera up, and shoot a few more quickly.
I often do this for team/group shots to get them warmed up. I'll say 'look at the camera, on three, one, two..." then take the shot. This always gets lots of interesting expressions and reactions, especially for those of the female side of life.
Keep shooting a few because those shots are great!
Then they are warmed up and you can shoot some more now that the first 'snap' is done.
Just some random thoughts.