Your essay should be inspiring to your reader - your teacher. He should receive a message that your essay is worth reading because there is something to learn from it. Even if it is a plain informative essay, you still have to inject a touch of inspiration into it. Your essay should also teach or educate, in one way or another, even if it is a plain entertaining essay. It could also serve as an eye-opener.
One thing you need to do to come up with a good essay writing is to spell it right. With the existence of word processors having spell check features, nowadays; there is no excuse for bad spelling. In fact, it has always been a MUST. If your piece contains bad spelling then no one is going to take your writing seriously. Good spelling has always been essential in good essay writing and there are no exceptions for that.
Writing is a creative endeavor that follows some set of rules. When you are writing, you can play around with these rules and there is nothing wrong with that for as long as it works. Actually, what people want when they read is to be amused, touched, or learn something. It does not matter if there are a few mistakes or if you have use grammar rules creatively on your write up; it generally do not ruin a good piece of creative writing anyway. However, when you are doing essay writing for your education, you are not suppose to bend the rules too much. Your writing need not be a masterpiece, but it has to be an enjoyable read.