I would like to improve my English, but how?

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I never realize my English backward greatly until my tourism in Korea in March this year. In Korea, I only communicate in English, but when I speak to others, my brain goes empty and I couldn's say a complete sentence but a words. Maybe they could understand what I said, otherwise, I felt terrible and amazed. How backward my English become, my god! Thinking those years in the university, my English was very good, no matter the vocabulary or the grammar or the oral. How flies the time, I have graduated for 5 years. During the 5 years, I very seldom learnt English any more, so it is father and farther away from me. Nowadays, I learnt English everyday,e.g. reading or watch the movies, but I find I have forget many words even the very very very commo ones. All of a sudden, I feel confused. I wanna save my English, but it's more difficult than that in school. WHAT CAN I DO NOW?!!!