Further divide these divisions into sub-divisions. These will probably be points for your paragraphs. The introduction introduces the reader to the topic and to the points you want to develop. You should summarise the overall theme of the essay and indicate how you are going to present your argument. This gives the reader an idea of what to expect and increases his comprehension.
Some students prefer to write the introduction last in the light of the material already presented.
The middle or body is concerned with the development of your argument. Present each major point and develop them with 2 or 3 paragraphs, by giving examples, citing research etc. Try to connect each main idea with some bridging statements. The conclusion should be a concise tying together of the previous points to form a logical outcome which adds something to the essay. You may wich to draw some implications from the research, offer some tentative answers or indicate direction for further study.