And take a class in English writing for business. Buy an English language newspaper or magazine and read it each week.
Fix a meeting once a week with a native English speaking friend and get them to read over your written work that week and explain where your errors lie. For example, in the question above you use "Not from English speaking countries?" The correct usage is "not from an English speaking country?".

Little things like this give away your origins and so learning from these errors will help you improve.