You have me at a disadvantage here Utkarsh. I am not sure if you want this essay to be graded on a TOEFL, IELTS, GRE, or PET level. My indecision lies in the fact that you did not specify this to be an exam essay and also, what kind of exam you are taking.The main components for the general scoring of an essay, regardless of the exam type normally fall within 4 - 7 categories. However, the 7 category judgment is normally used in a PET test, which I doubt you are taking so your essay would be judged on 4 criteria which would (normally) be as follows (Similar criteria for TOEFL and IELTS) : Task Accuracy, Lexical Resource, Cohesiveness and Cohesion, Grammar Resource and Accuracy. The most important score here will be the first one, which is task accuracy since you need to show that you can understand and deliver your work based upon English language instructions. If you fail the task accuracy part, you will find it hard to bring up your score in the remaining levels.
Now, if you asking me how the essay will be judged by a reviewer, then that will all depend upon the qualifications that you present. Nobody really knows how a reviewer judges an essay but it is normally judged based upon merit, the opinion of the reviewer, the school criteria for its applicants / scholars, and the supporting documents that you present. The essay is only a form of pre-interview that, when combined with your other documents creates the basis of the considerations for your essay and possible scholarship.