It's very important to write on one side of the paper only, believe it or not. This may seem trivial or tree-wasting to you, but I can tell you honestly that it always irritates me when I get an essay written on both sides of the paper, and I know that I'm not unusual in this. If you write professionally, as an author or journalist, you ALWAYS write on one side of the paper only. And do you really want to irritate the person who's marking your essay??