Can you suggest a good teacher to help me to improve business writing skill?
I can't suggest a teacher, but I can suggest you write any troubling passages here for some help in making them better. There are several books on effective writing (a key first step for effective business writing) and then on the more specialized aspects of business writing. I believe in a prior post you said you are in England; I just read a review of a book by an Oxford professor called simply How to Writethat gave it favorable marks.