One age-old example of a good essay exam item is: "Make up a questionand answer it." I tried using that item...once, and most of the studentsobjected vehemently that the item was unfair, that they did not know how to make up good exam questions. Their job, they said, was to answerquestions, not ask them! From that time on, I have required my studentsto write exam items as a part of their assignment. I assure you thatwriting and answering items is a very valuable tactic in preparing forexams.
If in doubt, you can even ask your instructor where you could find an example of a good essay, one they would approve of and see if they can give you any leads.
Find an example of a good essay to study
Basically, there is no only and one example of a good essay. A lot depends on the one who will read your work. Different people have different tastes. So, consider that as well and do not forget to take recommendations before writing. Style, volume and maybe even some ideas can be given by a teacher.