Leave a space after a comma and a full stop - always.
Practice your articles - 'a', 'the'
Don't start an essay like this:
"Should a city do A or B?".
"Recently, there has been much debate about whether a city should do A or B . Some people believe that a city should do A, whereas others believe that B should be done."
Think of an opening which the other 3 million students haven't written.