Agreed that consistency is the key, not just with English but with any subject. But, practise essays in the weeks leading up to the exam won't hurt. Ideally by then they will serve as ways to finetune your responses as well as time management.
I think you can also help develop greater depth in your responses by picking out a random page in one of your texts, read it, and ask what does the writer do and why? This is probably more Lit related, but it could be a useful excercise. Why does the writer talk about the plant in the corner of the room? Do they adopt a tone? Do they use language in an interesting way? Do the characters talk in a certain way? Just keep asking why and find your own answer (or if you can't, discuss it with others).