When editing, make sure to pay careful attention to:
Substance refers to the content of the essay and the message you send out. It can be very hard to gauge in your own writing. One good way to make sure that you are saying what you think you are saying is to write down, briefly and in your own words, the general idea of your message. Then remove the introduction and conclusion from your essay and have an objective reader review what is left. Ask that person what he thinks is the general idea of your message. Compare the two statements to see how similar they are. This can be especially helpful if you wrote a narrative. It will help to make sure that you are communicating your points in the story. Here are some more questions to ask yourself regarding content.
Have I answered the question asked?
Do I back up each point that I make with an example? Have I used concrete and personal examples?
Have I been specific? (Go on a generalities hunt. Turn the generalities into specifics.)
Could anyone else have written this essay?
What does it say about me? After making a list of all the words you have used within the essay — directly and indirectly — to describe yourself, ask: Does this list accurately represent me?
Does the writing sound like me? Is it personal and informal rather than uptight or stiff?
Regarding the introduction, is it personal and written in my own voice? Is it too general? Can the essay get along without it?
What about the essay makes it memorable?