A forbidden word when doing portraits, especially of men: “SMILE!”.
I say that for two reasons. First, you do not necessarily need a smile in every portrait. Art portraits, glamour: fashion, personality: there are many categories that do not need (that actively should not have) smiles.
Secondly, people, especially men from age two upward, are usually not good at smiling on command.
Here’s me, photographed the other day by student David Forster in his studio, using his D90:
That is kind of a wry smile – and it certainly works, for me. If David had called out “smile” I would have looked much more awkward.
If you want smiles, make your subjects smile – do not tell them to smile.
The shot was lit with speedlights with Honl Photo modifiers: a grid for the background light, and a snoot for the hairlight. A softbox was used for the mainlight and an umbrella for the fill light.