@Falcon,
Essay writing is an important subject in the CSS subject list. Most people consider it a difficult one but it is one of my favorite subjects. So, I won't let you horrify saying, that it is the most complicated subject and students hardly qualify it.
It's not difficult but laborious as it demands keen research on the topic.
Now come to, how to attempt an essay.
Whenever you hold a pen for writing an essay (on any topic), imagine you are going to tell your examiner each and everything about the essay and he/she knows nothing. (Examiners know more than you, I have said imagine). Prepare every essay thinking this.
For gaining comprehensive knowledge on the topic a single source ( book on the essay) may not be sufficient. You should search for your topic in magazines, newspapers, tutorials, and discussions as well.
Now, craft an extensive outline that covers the topic completely.
Write an essay in paragraphs with no headings.
Take an engaging and catchy start and the whole attempt should be well organized so you can grab the examiner's attention from beginning till last.