I lived in South Korea until I was 21 and then I went to the USA to study.

I've been here (for) almost a year but I don't feel like my english skill is improving.

for can be omitted here, but I think it sounds better with the "for" included.

I lived in South Korea until I was 21 and then I went to the USA to study.

I've been here for almost a year but I don't feel like my eEnglish skill is improving.

I know I have to study hard If I want to improve my skills in English but I haven't done that,; so from now on, I'll write about my day every single day.

My dDay

Title capitalization rules

I study in Texas, USA, but my eEnglish skills are not very good.

Nationalities and languages are always capitalized => English

I lived in South Korea until I was 21, and then I went to the USA to study.

I've been here for almost a year, but I don't feel like my eEnglish skill iss are improving.

Your skill in English would generally be pluralized => English skills

I know I have to study hard Iif I want to improve my skills, but I haven't done that, s. So from now on, I'll write about my day every single day.

I'm studying in Texas, USA, but my eEnglish skills are not very good (or "my English is not very good").

I lived in South Korea until I was 21 and then I went to the USA to study.

I've been here almost a year, but I don't feel like my eEnglish skill is improving. (or "I don't feel like my English is improving")

I know I have to study hard If I want to improve my skillEnglish, but I haven't done that, so from now on, I'll write about my day every single day.

I think it sounds more natural to say "I haven't been doing that" instead of "I haven't done that".