I have stated these many times for the past 10 years.
First, watch without opening sub. Then watch with sub, make sure to use pause function to look up unfamiliar vocabs and understand them all. The last step is to watch with no sub as many times as necessary until you can at least understand 90%.
Another suggestion, try watching classic/epic movies as the dialogues are great and the actors speak very clearly. Ben Hur, Cleopatra, Casablanca, Sound of Music, Clash of the Titans, Lord of the Rings, ET etc.