Being physically in the environment where you have no option than using English would be the best, obviously. If you are a student, I would say, save as much as you can for a while and spend a year or two in those countries even it can be a huge investment to you because it will pay off later.
Otherwise, watch a season of your favorite TV show multiple times with English subtitle on. At first, you will have to read the text but, after a few times, you will be able to listen and understand the conversations. Wish you the best luck with your study, mate.