Before you apply to graduate or professional schools, you should seriously think about why you are seeking the particular degree and why you want to apply to the institutions you have selected. Keep in mind that applying to graduate school differs from applying to undergraduate school in that you should be trying to identify individual programs and not simply prestigious institutions that will serve you well. If you only focus on the institution, not the individual department, program, or professional school, you might find yourself overlooking superior graduate programs and applying to programs that are not a good fit for you and for which you are not a good fit.
Why are admissions essays important?
The admissions essay is a part of the application that can make you stand out as unique even among a large group of similarly qualified applicants. It provides an occasion to establish your own personal voice, and to explain yourself why you are well suited to the programs you are applying to, rather than relying on the opinions of others. You might think of it as an opportunity something like a personal interview - only you get to reflect for longer over your written presentation of yourself.
What are they looking for?
The people reading your applications are much more interested in your intellectual or professional development than in your personal development. This certainly does not mean that you need to write an impersonal essay - you should write in the first person, and what you write should be an essay that another applicant could not write. But generally if you write about your own life story it should be because it is particularly unusual and relevant to what you will be doing in graduate school.
Your aim is to convince those reading your application that you are prepared for graduate study and able to do it well, that you are interesting enough to have something to contribute, and that you are sufficiently focused and committed to stay the course. In order to do this you should not simply produce a list of your accomplishments; they are important, for sure, but it is best to focus on a few specific ideas, experiences, or themes. In this way you can go into some detail, and give a much better idea of who you are and what you have learned than if you tried to cover everything briefly and vaguely. For example, rather than merely claiming to be interested in research, it would be great to be able to explain a research project you have produced or participated in; rather than just saying you are committed to the betterment of humanity, show how you have demonstrated that commitment.
Before you apply to graduate or professional schools you should have given a lot of thought to why you are seeking the particular degree, and why specifically at the institutions you're applying to. You should show in your essay that you have done this thinking and research, and explain to the schools or departments why you are a good fit with them. This means saying something about the school that could not be said about most other schools. For example, instead of writing "you have a very strong faculty," mention some examples of faculty research that interest you. You could be the most excellent of candidates, but if you said that you wanted to focus on something in which no faculty at that school were interested, you still might very well be rejected. Conversely, showing that your interest in a school is well-informed and carefully thought through will help your chances. This does not mean that you need necessarily write an entirely new essay for each school you're applying to - you can write one master draft, and then alter parts of the essay as needed for each school. (Make sure you double-check that you have used the name of the right school in each essay!)
You should also be able to state what your goals are. If you're applying to a doctoral research program, you should explain at some length the field or fields that you are interested in getting into (it is not a terrible thing, in the humanities and social sciences especially, not yet to have your mind fully made up, and to be interested in exploring more than one thing - you do still need to show you know enough to outline a possible field of study though). If applying to professional school, you should explain what area of the profession you see yourself getting into, and how you see the degree as helping you to get there - again, it is not necessary to be narrowly specific; in fact it is good, up to a point, to show that you are broad-minded and flexible (but again, you do want to make clear that you have thought through your choice carefully).
Should I mention any weaknesses in my application?
If you know there is some striking weakness in your application - perhaps a GPA or score that is glaringly low, or some long gap in your resume - you may want to account for it in your statement, rather than letting the imaginations of admissions officers run wild. (Having a few Bs does not count as a striking weakness; but if, for example, as a result of suddenly needing to work a 40-hour week to support yourself, your grades slipped significantly, that might well be something to address). You should make sure, though, that you explain it in terms as positive as possible - for any problem, show that it is safely in the past and will not recur again in graduate school. If you struggled at first in school, but your grades have improved every year, or your grades in your major are particularly outstanding, these are things you could point out - but again, be positive; avoid apologizing for grades you might consider low. Some people suggest including such explanations only in a separate addendum, in order that the tone of your essay is uniformly positive.
Where should I start?
This will not come as a surprise to you, but it is, nevertheless, extremely important - read the questions! If you neglect to address a specific question, or fail egregiously to follow directions about page or word limits (2-3 pages is normal, but check), your attention to detail is unlikely to impress. Usually you will be asked fairly generic questions about your qualifications and aims for graduate school, but of course you need to make sure.
When you first sit down to write, my advice is not to start actually writing your essay, but simply to jot down ideas. Write down a list of your goals, your achievements, your strengths and weaknesses, interesting experiences you've had, and how you plan to continue your academic or professional development. It doesn't matter at this stage if they are all things you would include in the final draft or not. It's better to be cutting down a long list of things to include when you write than to be struggling to find things to say. You might also ask friends and relatives for suggestions, to see if they see in you qualities that you would not think of claiming for yourself.
Once you have your list of ideas, you should still not try to write a perfect, formal essay right away - start very roughly and experimentally, to get an idea of what kind of narrative structures, themes, and examples work and which don't, before taking trouble over things like wording and sentence structure. If you take the time early on to craft fine sentences you will find yourself unwilling to delete them - and you want to start out as flexible as possible, to give yourself the opportunity to come up with the best approach you can.
Once you've figured out what you're going to include in your essay, and how to structure it in order to make it read as a unified whole, then (and only then) should you consider thinking about your writing style. This does not mean using a thesaurus to find impressive-sounding, unusual words (though it does mean trying to avoid clichZs). Quite the opposite in fact - a clear, direct style will best convey the impression that you are focused and clear-thinking. Do make sure your tone is enthusiastic and positive - this is not the place for excessive modesty or self-deprecation.
You do want your essay to stand out (whoever reads them will probably have to get through a painfully large stack of fairly generic essays; it would be nice for him or her to come across something surprising and engaging). On the other hand, you want to be interesting through the force of your ideas and the way you explain your experiences, not through gimmicks (doing absolutely anything to stand out, such as sending your essay in a series of fortune cookies, or putting it in limerick form, will not indicate that you have good judgment). Consider carefully how to open your essay. Many begin something like this: "Ever since I was a child I have wanted to be a marine biologist." While it's a perfectly good idea to try to explain where your enthusiasm for a subject comes from, you want to try to avoid such a common opening. Bear in mind that you do not have to narrate your experiences and achievements chronologically - you can start with some intriguing recent moment of inspiration, and then move backwards. Do get straight to the point - don't start with something like "Please allow me to introduce myself." Some people open with a quotation - personally I think it's much better idea to begin with your own words. Open with a bold, declarative (but not banal) statement, or an interesting detail or anecdote. Also when you conclude, you do not need to thank the admissions committee - it would be great to conclude pithily, perhaps with a statement that connects back to your introduction, or to whatever theme runs through your essay.
I have a final draft - now what?
Have as many people read it and give you feedback as possible. (Show it to me to start with if you like, or take it to the Writing Center (THH 321), or show it to friends or relatives.) If at all feasible, it makes sense to include among your readers some people in the field you're trying to get into, since they will have the best idea of what will go over well in their subject area. Give a draft to your recommenders - it will help them understand how you are presenting yourself in your application, and they may also provide you with useful feedback. Of course you may get conflicting advice from your various readers; if that should happen you will simply have to use your own best judgment as to what advice to accept.
When you have completed your absolutely final draft (and you should have written several drafts before that point), your choices about font and character size should be determined according to what will be most readable. You should also proofread carefully!
Boy, that's a lot to think about!
Yes it is. That is why you should start early, and take your time. Many people hurt their applications by waiting until the last minute to write their admissions essays, and writing one rough draft at best, with little or no input from other people. Do not be one of those applicants.