How would you shake my hand? Or that of my sister?

I’ve been taught, when shaking someone’s hand, to give a firm one when meeting a man, and less firm when meeting a woman.
However, sometimes i shake a man’s hand and in return i get a weak shake back.
Do you decrease the strength of your shake when that happens to balance it?
Or when you shake a woman’s hand and you get a much more firm shake back, more firm then you would expect, do you increase the power of your handshake?
So, i would like to know how i deal with that in the given circumstances.
And what is your shake etiquette?