Answer:
Your in luck, I just had pretty much the exact same essay question and got an A for it. That is a weird coincidence though, i had 'How does Stevenson explore the complexites of human nature and the concepts of good and evil in his novella 'The Strange Case of Doctor Jekyll and Mr. Hyde?' anyway you didn't need to know that so here's my proper answer:
Write about:
The description of setting- how they refect the charectors, the laboritary, Soho etc. eg. Dr. Jekyll's house looks nice and ordinary on the outside whilst his laboritary is a horrible building and you couldn't tell they were the same building from the outside and yet they are.
The Narrative Style- How it is written from three points of view; Mr. Utterson's, Dr. Lanyon's and Dr Jekyll's.
Charector Flaws- none of the charcetors are perfect, Mr. Hyde is pure evil but Dr. Jekyll is not pure good because he keeps turning back into Dr. Hyde because he enjoys it. Dr. Lanyon and Mr. Utterson arn't perfect either they talk about 'growing curiosity' and how even they find it hard not to want to know the truth on the spot, they are impatiant. Mr. Utterson is also nosy and antisocial sometimes.
Physical appearance- Dr. Jekyll is big and handsome where as Mr. Hyde is short and gives of a feeling of deformity, what does this signify? Only a small part of Jekyll is evil?
To be honest you can get away with just about any nonsense in an English essay as long as you bakc it up with evidence. Personally i don't Stevenson ever intended for his work to be anylysed so closely. These essays are pretty pointless anyway. When my English teacher was explaining it she started talking about the importance of doors and windows and how Jekyll was like a door and Hyde like a window, but if you tried that hard i think you could turn any fictional charector into a window.
Name a fictional charector I'll explain why they are like a window for you.
Anyway i hoped that helped, that was the kind of thing i wrote and it seemed to be what my English teacher wanted to hear.
Hope it helps