Firm, but not with a macho display of pressure.
I had a guy do serious damage to my wrist, once, when I endeavored to shake his hand, out my driver's side window, as I left his property. This guy stood 6'5", and weighed around 235 lbs. He squeezed my hand so tight, while turning my wrist, that I'm sure my tendons were injured.
Growing up in the country, my closest friend up the hill used to take joy in squeezing the crap outa my hand
Thing is, wunna his chores was milking their cow
By hand
Had a hell of a grip
I didn’t have a cow
And his hands were bigger than mine as he was a bit older, and stronger
It became a contest
After a few excruciating grips, I noticed he’d always kinda get the jump on me
So, next time I got the jump on him, shoving the crotch of my thumb into his, but a few degrees to my right,
enabling me to level out the odds in the crushing of the last knuckle that connected the little finger to the hand
I also learned I could administer greater pain if I moved that knuckle back and forth
Not so much fun for him
He moved on to arm wrestling and starting fights
And became some sorta tough biker guy
I moved on to babe wrestling and avoiding fights (not much success at either)
And became the sweet lovable guy I am today