“A breath of fresh air”

“Get out of hand”

To become uncontrollable.

“Speak of the devil”

The person you were talking about appears.

“Piece of cake”

Something very easy to do.

“Fish out of water”

Feeling uncomfortable in an unfamiliar situation.

“The tip of the iceberg”

A small visible part of a much bigger problem or situation.

“Take it with a grain of salt”

To not completely believe something.

“The best of both worlds”

A situation where you enjoy two different advantages.

“Rule of thumb”

A simple practical rule based on experience.