Asslam-o-Alaikum Here are some useful guidelines that can help you in Essay-Writing.
1. First of all, Study is the prerequisite for essay writing. Keeping in view the recent essay trend one should do a lot of study on various topics . Everyone who have developed a good habit of book-reading can develop interest in these subjects easily. Now coming to the point that which books one should read and how much study is necessary.
1. Try to read every book that fascinates you. I am mentioning some topics that will help out in increasing your knowledge for essay.
a. Modernism and Post Modernism
b. World History (Revolutions, Geography, Wars, Peace Treaties)
c. Communism, Marxism, Socialism, Capitalism, Fascism (Just a brief idea of these things)
d. Nations and Their Narratives
e. Religion and World (Focus on Islam)
f. Social Issues and Social Needs and Social Evils (Education, Human Rights, Governance System e.t.c)

This all seems to be a lot of work but once start this thing and you will make your way. There is another way. See topics of essay papers from (2000 - 2015) and start preparing there outlines. It will also help you. (My habit in last days was that I read topics related to essay given in past papers from different books and It helped me a lot in attempting an essay) .I will suggest some books as well to read if anyone is interested to do so. It is not necessary to read the whole book daily or read books for like three months and then focus on other things rather read two to three pages daily or read some specific topic daily. It will hardly take an hour. Make it your habit and feel the change. In the next thread I will Insha ALLAH explain the method of preparing outline. Good Luck