Take it with a pinch of salt
Don't take it too seriously. Example: "I heard elephants can fly now, but Sam often makes up stories so I take everything he says with a pinch of salt".
Hit the sack
Go to sleep
Under the weather
Sick
It's a piece of cake
It's easy
hold your horses
wait a moment
break a leg
good luck
Let the cat out of the bag
Give away a secret
Spill the beans
Give away a secret
It's raining cats and dogs
It's raining hard
Once in a blue moon
Something that doesn't happen often. Example: "I remember to call my brother once in a blue moon".
You can't judge a book by its cover
This person or thing may look bad, but it's good inside
Give someone the cold shoulder
Ignore someone
Hang in there
Don't give up
See eye to eye.
To agree. Example: "We don't exactly see eye to eye about the best basketball team".
Beat around the bush
To avoid talking about a topic.
The ball is in your court
It's your decision