4. Use subtitles
The first time you watch something, I'd highly recommend that you use the english subtitles.
Like with the song, you can first read along as they talk. Not only will you follow the conversation better, but you will understand it better too!
In the beginning, you'll be unable to help yourself looking at every word that appears and you'll get confidence with the dialog.
Then, watching at it a fourth, fifth time, you'll be able to understand the dialog withouth checking the subtitles.
As your understanding improves, you'll be checking only a word or two and will be able to perfectly understand the global meaning of the ideas they talk about.
Don't be desperate! Accents, speaking speed, unknown words are a wall you need to address, but, remember, you weren't able to do things the same way when you were 8 or when you are 13, right? That's the same process: evolution, experience, studying … The more you do, the better you get!