Idiom meaning “to relax or calm down.”
Take it easy
Proverb meaning you should not give up.
Never give up !
Phrasal verb meaning to relax.
Calm down 
Common collocation with “calm”.
Stay calm
Idiom used to say someone should not be so serious or angry
Lighten up
Proverb meaning practice helps you improve.
Practice makes perfect
Phrasal verb meaning to reduce speed or intensity.
Slow down
Collocation meaning polite communication.
espectful conversation
Modismo que significa reducir la tensión en una situación.
Romper el hielo
Proverb meaning it is good to be honest.
Honesty is the best policy
Phrasal verb meaning to avoid conflict.
Back away
Collocation meaning to reduce stress or conflict.
Lower tension
Idiom meaning to stop pushing a topic too strongly.
Back off
Proverb meaning working together is better.
Two heads are better than one
Phrasal verb meaning to reduce pressure or effort.
Ease off
Collocation meaning a careful reaction.
Measured response
Idiom meaning to accept information calmly, not fully believing it.
Take it with a grain of salt
roverb meaning it is better to act than only talk.
Actions speak louder than words
Phrasal verb meaning to manage a situation calmly.
Deal with
Collocation meaning solving problems peacefully.
Peaceful resolution