Include an introduction and a conclusion no matter which method you choose to structure the body of your essay. It is often helpful to write the introduction and conclusion after you have written the body of your paper. A good introduction will introduce your subject in a general fashion and then begin to narrow gradually, ending with your argument. Think of it as a map of the rest of your essay. The conclusion should return to the ideas with which you began your essay and restate your argument. It should leave your reader with a summary of your main points as well as your argument.
In 2009’s mains attempt, I got only 20/200 marks in the Essay. It was about ‘are we a soft state?’ . I wrote it only from the foriegn policy and law-n-order point of view, without seeing the cultural -historical contexts. It was a monotonous essay without any spark. Moral of the story: do try to see different angles of the subject and give a thorough thought before you start writing.
Some veterans are in opinion that you should pick up the essay on technical subject, example space-technology, advances in medical science, how IT has changed lives and so on. Because only a few people attempt them, and due to technical nature, your ideas are unlikely to be in conflict with the examiner so you’ll get more marks.
But then again you need enough ‘content’ to write 1500+ words else the padding route=digging your own grave. And there are enough toppers who wrote the non-technical essay and still got in the top-merit list so as usual for every generalisation made about UPSC, you’ll find a counter example!