Check a dictionary.

There are a lot of lists for common idioms. So I will give you some Australian ones: "Don't give me the raw prawn" - Don't lie to me "You're mad as a cut snake" - You're crazy and not making sense "Your blood is worth bottling" - A compliment. Saying you're doing something so well you're worth keeping. "She'll be apples" - Everything will be ok. The Australians and maybe the British will understand these. No one else will...

I couldn't think of any off the top of my head, but I did find a good list: http://www.englishforums.com/content/lessons/20-most-common-idioms-in-english-and-what-they-mean.htm

put your foot in your mouth - say something dumb or awkward it keeps you on your toes - it forces you to pay attention all of the time it's raining cats and dogs - it is raining very hard jumping through hoops - going to a lot of effort to please someone money doesn't grow on trees - you have to work for it, you won't just find it hanging out, waiting for you