Give me suggestions to improve the American slang

I am planning to settle in USA,
But I know slangs/everybody over there talk so fast. I heard “pissed off’, “drive me nuts”, “heck”, “laugh my face off” and countless other words and phrases from movies that were totally unfamiliar.
I am thinking: “how can I learn to speak like this? I’m thinking I am pretty good in English.” But I need to learn American slang.
As an Global Minded person, Can you give me some suggestions to improve my American slang :)