1. A piece of cake: something that can be easily done.
I think I got an A on my Spanish test. Truth is, I´ve studied hard for it, but it was piece of cake.
2. A taste of your own medicine: when you are mistreated the same way you do it.
Susan´s always bossing her coworkers around, but when the boss is here, she has a taste of her own medicine.
3. To pull the plug: to stop something from happening or continuing.
"The government pulled the plug on spending".
4. To know the ropes: to understand the details.
I have no idea what the problem with the car can be. I´d better take it to the mechanic, who knows the ropes.
5. To run out of steam: to be completely out of energy.
I´ve been working so hard lately that I do deserve these vacations before I run out of steam.
6. Saved by the bell: saved at the last possible moment.
When the teacher was going to call Bob to read his composition, the bell rang. This time he was saved by the bell, but next week there´ll be no escape.
7. Get over it:: to move beyond something that is bothering you.
They had been together for such a long time that when they broke up, it was really hard for Jane to get over John.
8. Dead ringer: identical, a duplicate (person or object)
He's a dead ringer for Bono from U2.
9. Bite your tongue: avoid talking (esp. something unpleasant).
"If somebody asks if you think there is something wrong with them, it is best to bite your tongue and say nothing".
10. When pigs fly: something that will never ever happen.
When pigs fly, then I´ll get a promotion on this job. Guess I´ll look for another one.