1. behind one’s back

Today we are going to learn “behind one’s back”. It means hiding something from someone.
A: Did you hear that Anne went out with Arthur?
B: I know. And she did it behind Bernard’s back!

2. Practice makes perfect

Another phrase is “practice makes perfect”. It means engaging in an activity again and again to improve the skills.
A: I just can’t speak English.
B: Practice makes perfect. It is true in anything.