If you are going to visit English speaking country it’s worth learning some English idioms. They will help you to look like an advanced speaker. As it said, unless you understand and use idioms in conversation you don’t know language. Well, here are some useful and frequently used ones:
To feel under the weather – to feel not very well;
To pull somebody’s leg – to joke;
To be on cloud nine – to be extremely happy;
Keep your hair on! (informal) – Calm down!