Idioms starting with C/D

Don't judge a book by its cover

Used to say that you should not form an opinion about somebody/something from their appearance only

Draw the line

To refuse to do something; to set a limit

Down in the mouth

Unhappy and depressed

Don't give up the day job

"Used to tell somebody that they should continue doing what they are used to, rather than trying something new that they are likely to fail at"

Don't count your chickens before they are hatched

You should not be too confident that something will be successful, because something may still go wrong