I'm Korean who is learning English. I think it's all same thing learning language. I can give you this advice to you. Don't push yourself to make a perfect sentence. I understand because I was like you before. If you wanna make long sentences, use '~고', ~해서, 했는데 like these. For example, 어제 극장에 가서 영화를 보고 있는데, 어떤 사람이 내 의자를 치는거야. 그래서, 뒤로 쳐다봤더니 무서운 인상의 아저씨가 앉아 있는데, 겁이 나서 아무 말도 못했어. (I went to movie theater yesterday. Somebody hit my chair, so I turned around who did it. There was a man who had a bad impression sitting behind me. I didn't say anything because I was scared.) Just practice everyday short sentences. And then, practice connecting two sentences using 고, 해서, 데 etc..etc..