It takes time and requires a lot of effort..
Try this way, it helped me..
From now on,
1. Talk/write in English for everything.
2. Do not feel embarrassed for making mistakes
3. Try to avoid meeting/talking with Korean friends until you become comfortable with English
4. Make English speaking friends, I started off with Indian friends first, and white later.. playing tennis together…
5. Try to speak a lot… be a talkative person.. and once you speak out wrong words/sentence.. you will realize how you should have said , and you will be able to speak correctly next time for similar situation… try to experience alot of situations…. the more you experience the sooner you become comfortable with English..