Do's and don'ts when writing in formal English

I will pinpoint some of the mistakes commonly made by my Chinese friends when writing in English.
I am not talking about writing e-mails or SMS, but writing in formal English in an examination or to your chief executive officer.
  1. Do leave a space after a punctuation mark. I see a lot of my friends don't do that and scrambles all the words in one page. I think mostly due to that typing in Chinese does not have this requirement. As a general rule one space should be left after a comma or a fullstop.
  2. Do check your spellings  After you finish writing, spend about 5 minutes to check the spellings. A lot of mistakes could be easily spotted. A little thing like this could mean a big difference if you are on borderline between a pass or a fail in an examination. If you are using Microsoft Word or similar software, do a spell check.
  3. Do make sure every sentence is grammatically correct. As a good rule of thumb, every sentence must have a subject, a verb and an object.
  4. Don't use slangs and try to avoid abbreviations. If you write to a person you know for the first time or to your superior, try to avoid using slangs, such as "it is cool" or "it is ok", as they are not acceptable in formal writing. Nowadays we tend to use a lot of abbreviations or acronyms (initials). Don't do that unless the abbreviations are generally acceptable (like e-mail, no one writes electronic mail). As for acronyms, please make absolutely sure that your readers understand them.