Speaking Fluent English and understanding native English speakers are two of the biggest and most serious problems facing most English learners.
The problem is often not a lack of vocabulary or a lack of slang. Many students are convinced that is the problem and keep learning more vocabulary. It's not the problem.
The problem is a lack of proper listening practice. Reading won't help you improve. Writing won't help you improve. Only listening will.
The challenge is you need to find something useful to listen to. This is key. If the material is too hard it is a waste of time. If it's too easy it's a waste of time. You need to find something that challenges you but isn't too hard. The speech needs to be just a little bit slower and clearer. The new words and phrases need to be explained. Other than that, it is important to be listening to native English speakers speak almost the way they do naturally. If you listen to enough stuff, you will improve. Most students don't and that is a huge problem. The worst part is they don't even know what the problem is and the waste so much time doing the wrong things.
I've spoken with many people who have a good vocabulary when writing an email, but can't understand it when it is spoken. They don't practice and it's killing them.
The second biggest advantage to improving English listening is that it will automatically teach you how to speak English fluently. Your brain will naturally learn to Speak like a native speaker. It sounds weird but it's true. That's how babies learn.
So Listen to something that challenges you and do it everyday
If you want a free PDF book for learning to listen and speak fluently go here and I'll email you one.