One of the most common issues I see when helping edit essays is stunted, awkward prose–that is, it feels, at times, painfully obvious that someone is trying to write an essay, rather than simply communicate. And that’s all, at the end of the day, an essay is: a way of communicating ideas via writing.
Now, that’s not to say you should write exactly how you speak–there’s a certain level of formality present in writing that there isn’t when, say, you’re talking with your friends. But it’s still a good rule of thumb to keep in mind: you want your writing to sound like a conversation with your reader–albeit one where you’ve had time to consider your words beforehand. A prepared conversation, of sorts.
This means avoiding several pitfalls. For example, if you have to refer to yourself when writing, use “I” and not the awkwardly formal “we” or “one.” Using “I” is something you should check out with your specific instructor, as some genres (and some specific people) find the use of “I” a bit too informal. But, in general, it makes your writing sound more engaging and enjoyable; it feels like you’re a specific person giving your opinions and thoughts if you use “I,” whereas if you use “one thinks that…” you sound like corporation, detached from any personal stakes in the essay.
Now, in some sorts of writing–such as reports where you’re representing an entire lab or department–“we” is actually preferable. But in many of the essays you’ll have to write in English class and the like, a bit of the personal touch can go a long way.
Similarly, if you’re one person writing the essay, you should write it to one person. Remember, you’re going to have an audience that will read the essay when you’re done with it. You need to ask yourself why this person is reading your essay, what they already know (or believe they know) about the topic, and what level they’re reading it at. You wouldn’t explain the same topic to your teacher and to a 4-year old.
You need to keep your audience in mind are you trying to convince someone who already has a background in the subject? Inform someone who has never heard of your topic before? Is it intended for academics, or the general public? All these things will affect how you will want to write. You don’t address your grandmother and your best friend the same way, and, similarly you shouldn’t treat your essays the same across the board.