I, You, We, He/She/They

(updated 3 May 2019 for gender pronoun inclusion)
I

You may use "I" when writing for me if you need to, but only if you need to. There is no need for the stuffy and convoluted "This author sees an important connection between war and cultural production." It's okay to write "I am convinced of an important connection between war and cultural production." What you don't want to do is weaken your statements with "I think" and "I feel" - "I think that Frodo is an anti-hero figure because he is small and inexperienced, and defies the norm of strength and skill in battle, but he has courage and compassion" sounds like you haven't made your mind up yet. Write it that way if it gets you where your going, but then go back and delete the weakening words "I think" so that you have "Frodo is an anti-hero figure because he is small and inexperienced, and defies the norm of strength and skill in battle, but he has courage and compassion." There. You're sure and you say so and now you can prove it.

You

Use "You" if you are directly addressing your reader, and in no other circumstances. Please, in formal writing, do not use "you" to mean "one." To write "When you first go visit the Dean of Students' office you will probably be nervous" is much too casual. Instead, put the noun you actually mean: "When students first go visit the Dean of Students' office they are probably nervous." If you are trying to find a general, inclusive pronoun, use "we."

We

If the audience for your essay could reasonably be included in a "we," then use "we." Instead of "When anybody reads The Great Gatsby they are struck by the charm of the main character," or "When you read The Great Gatsby," etc. etc., try "When we read The Great Gatsby we are struck by the charm of the main character." It helps to create inclusiveness, and helps dodge some awkward pronoun gymnastics: "It is important that we recycle because the world cannot continue to replenish our natural resources at the rate at which we are using them."

He/She/They

When speaking in hypotheticals, we are first tempted to go for singular pronouns - perhaps this is a very human instinct to not overreach on something unproven. I don't know. I do know that using single pronouns for anything but determined, designated single nouns becomes tricky before you know it. Example: "When a student goes to visit the Dean's office he or she may find that he or she is nervous about the outcome of his or her visit."* Terrible. Clunky and awful. No one wants that. 
And so too often we avoid the he/she stuff by turning to a plural pronoun there - they.  Our example becomes: "When a student goes to visit the Dean's office they may find that they are nervous about the outcome of their visit." But this is incorrect because the original pronoun was singular, unless "they" is the preferred pronoun of the person being referred to. 
If you know the preferred pronoun of the person, use it. I, for example, prefer she/her. So if you're talking about me going somewhere, say "When the professor goes to see the Dean's office, she may find that she is nervous about the outcome of her visit." (I'm not, though - I love my Dean.) If you know that the person you're referring to prefers he/him, use he/him. If you know that the person has asked for they/them, then please use they/them. In that situation, they/them is correct. If we are referring to a student who is, perhaps, transgender and has requested the they/them pronouns, we would write, "When the student goes to visit the Dean's office they may find that they are nervous about the outcome of their visit." Although, again, they have no reason to be, because the Dean is delightful.
But, often the issue is that we are writing about a hypothetical person, or people. In such a case, make the original noun plural, and you're all set. Fixed example: "When students goes to visit the Dean's office they may find that they are nervous about the outcome." (The end got tricky, because I had to make it "their visit" which looks like they're all visiting at once, or make it "their visits" which could mean that they each visit multiple times, heaven forbid. So I just dropped it since it wasn't strictly necessary).





*A bit of history: There was a time, dear students, which you will not remember because it was approximately well before you were born, when people in groups were referred to as male if there any men in the group at all. When I was in college, all students, in all brochures and handbooks, were referred to as he, him, his, etc. This was not if anyone was referring to a specific female student, of course, but when talking about a typical, hypothetical student, they would say or write male pronouns. It was this way in all Western communication (business, government, etc.) and had been that way for pretty much ever. A brochure from my college, or from a church or company or organization, would read something like this: "Any student wishing to consult with his advisor should contact his advisor directly" or "Any member wishing to upgrade his membership should consult the guidelines" or "If an employee must take extra sick days he should discuss this with his supervisor." That was just life. (I had friends at all-girls colleges like Agnes Scott, where this was not the case, who said it was a relief to finally hear themselves referred to as she, her, and hers). A cultural movement in the early 1990's, generally called "Political Correctness," worked to change this, along with eliminating official terminology that doubled as discriminatory slurs (all disabled people used to be labeled "retarded" - officially - and I'm not kidding about that). Political correctness was deeply hated at the time and still is by some, and it was a huge mess getting a cultural consensus around how to use language both effectively and respectfully. We went through some awkward times when we had to write "he or she" each time we used a hypothetical. It took us a while to get around to plurals. I say all this because it really is that important that we get our pronouns right, because in this case "right" means "respectful to the existence of other human beings." Political correctness accomplished wonderful things, not the least of which is college brochures that acknowledge female students along with male ones.