Start early
As soon
as you are given an essay question, begin your thinking. If you don't, you
might miss useful information whilst doing other research. The television and
radio often have programmes on topical issues which could be of use - if you
don't already have some ideas for your essay you could miss their usefulness.
It is similar to the process when you learn a new word: because you have
actually looked it up, it then seems to appear more often. This is because you
become more sensitive to it - the same will happen with your essay subject.