You can't judge a book by its cover.

It’s raining cats and dogs

Break a leg!

"Don't beat around the bush" - I actually posted about that this recently if you would like to have a look at my profile I also like :killing 2 birds with one stone" Happy learning

Some of my famous idioms are, 1. It's a piece of cake. 2. Kill two birds with one stone. 3. It's raining cats and dogs.