Before you begin, make sure you know the word limit for your essay. You will usually be given a definite number eg 1500 words or 2000- 2500 words. If you are given a fixed number, it is usually acceptable to write 10% fewer or 10% more words. If you are given a range, try to stay within that range. However, check this with your tutor as you do not want to be penalized.
Remember that the introduction denotes the first paragraph of your essay that should be a short paragraph in which you should develop the points related to the subject of your essay. It should make the reader interested in having a further look at your piece of writing.