Faire d'une pierre deux coups is a proverb about getting things done in a efficient way. The Englisn equivalent would be To kill two birds with one stone. It's when you succeed to accomplish two things at the same time, instead of one.
Let's see some examples:
In French: Je ferai d'une pierre deux coups: en allant au travail, je passerai par la banque pour payer la facture d'électricité.
In English: I will kill two birds with one stone: on my way to the work, I will go to the bank to pay the electricity bill.
I hope you find this expression useful and maybe you will use it in some situation :)
