According to Cambridge University's English as a Second Language department, which trained me as a teacher, you will need about 600 hours of classroom instruction + homework. You'll also need to practice, practice, practice, and practice some more.
It will also help if you spend a lot of time reading, as reading is very, very important for learning vocabulary. You'll also need a lot of practice speaking.
But here is the most important thing: you need GOOD instruction. Good instruction always involves input (reading/listening), practice using the new language, and production (= speaking or writing practice) using the new language. We can change these to production -> input -> practice -> production, but a GOOD English lesson must always have input, practice, and production.