The trick is to write an essay or two with no prior knowledge about the given topic. It might put you under a lot of stress but it's for your own good. Manufacturing something out of nothing is the greatest asset that almost everyone has, albeit on different levels. It would also bring out your general opinion on a given issue and make it easier for you to make a smooth transition to your essay.

It would give you a general idea on how to organize your ideas and form a basic structure to your essay.

Last but not least, have some self-confidence and give it a go!