I started by reading the English WWW and then participating in English forums. All video games had synchronization in my native language. But I started to deliberately play them in English with subtitles. And then I started to watch more and more videos and movies in English (with subtitles when available). Now I only need subtitles occasionally to offset unclear speech.
Starting with text makes looking up unknown words practical. Games most often let you take your time to read text. Cutscenes can be problematic early on. But games often support setting different languages for audio and text/subtitles.
Being in an environment speaking the new language would probably be the fastest way.
What did not help at all was having English taught in School. Memorizing vocabulary and working through artificial text book did not work at all for me. Only when the internet entered my life years later, did I actually get a hang of the language.
P.S.: English is the universal language right now. Even Chinese children learn it in school. I think, it's possible to get away with only speaking English in basically any industrialized country. Not everyone will be able to understand you. But there will always be someone who can translate.