Essay has three parts.
Introduction (a short intro for your essay), Body (write here the info's you gathered about the theme/topic), Conclusion (a short conclusion, usually, you just wrote here things you wrote at your intro but rephrased and in different way).
Know things you need to know about the topic given to you, (for body). Make sure that your intro is so attractive that will make the reader interested to continue reading your essay. As possible, make your essay so deep that will make it that beautiful, usually, some people, especially critics and teachers, like essays like that, that even make them interested. Also, go straight to the point, don't make your essay that long, unless you've gathered a lot of info's or thought a lot of ideas about the topic.
☺ I hope it help.