It would be a good start for u to watch films, TV programs or read any articals which is in english and also u r interested, so u won't get board. This'll help u to build up some sort of sence of how the native speaker or writer get the sentence done. And that will solve ur grammar issue literally and improve ur writing significantly but only works in long term. By contrast, u can take a course or sth like that if u want to improve ur grammar in short term, but loads and loads of home work r requested. And that's gonna be tough 4 u. After all Roman doesn't built in one day. Happy learning and good luck.

Hello, I'm from Korea and I wasn't good in English grammar neither. I decided to go to Manchester to learn English in real life and found a school called MCA Languages. I stayed there for 3 months, taking classes 20 hours per week, and became fluent. I really think that the best way to learn is to travel and practice with locals. I advise you to check on their website if you're interested! ;-)