First notebook entry: Introducing myself

Hello,
I used to study English when I was a student.
But, It's not enough for me, because sometimes I need to talk in
English in my Office.
So I want to practice and study English.

Good work! The agree with above corrections.  I'd like to share how I would write this notebook entry:

I studied English when I was a student.

But my English isn't good enough for the times I need to speak it in the workplace. That's why I want to practice and study.

First notebook entry: Introducing myself

Hello,
I used to study English when I was a student, but It's not enough for me because sometimes I need to talk in speak English in my Office.
So, I want to practice and study English.

First notebook entry: Introducing myself

Hello,
I used to study English when I was a student; However, It's not enough for me because I need to speak English in my office sometimes. 
Because of this I want to practice and study English.