I still have to decide! ㅜㅜ Such a struggle

All I know is - hard!!!

Widen your vocab?

Read, write, listen, speak!

And scope a dictionary. 

You should be able to find and think of many many words you don't know. Then, practice using them.

Try describing pictures or using picture prompts.

Try making YouTube videos giving a tour of an area.

Try translating an article.

Just trying to do those things will make you realise all the words you don't know. Then, look them up and practice them!

Hmm I think grammatic words are also vocabulary. I'm sorry about that I couldn't give exact answer, but I saw many foreign learners recommend TTMIK (talk to me in korean) website.

@Edwin: 네! 나는 한국어를 배우고 있어요. But I'm finding it hard to widen my vocabulary.

@Edwin: 너가 배우기 어떤 언어 노력하고 있어요?

(Was I able to say it right? hehehe.)