This is very much a work-in-progress.
The task of a writer is not to merely write down their thoughts, but instead to provide a service for a reader. That is, think of your model as an instruction manual: something designed to make someone else's life easier. You are trying to explain things in a way that will help a reader understand what's going on. That guiding principle should inform every choice you make about how to structure your essay, how to explain particular ideas, and so on. Beyond that, here is a ragtag list of pointers:
- Each paragraph should make a single and self-contained point. If you don't know what that point is, something has gone wrong.
- Guide the reader with signposts such as "So far, I have shown that...", "I now explain my central argument", "But there is an objection we should consider...", and so on.
- Try to find ways to express your claims more concisely. This allows your essay to cover more ground, and makes it easier to read.
- Imagine your reader is intelligent, but does not know the subject at all. You'll need to explain any term that would be unfamiliar to such a person.
- Don't use a complicated word if a simple one will do.
- Some students try to avoid reusing words ("Descartes says __, Kant asserts __, and Bentham proclaims __"). Don't do this - it's ok to reuse the same word multiple times! Doing so is often clearer: the reader has no clue whether you are using a different word to mean the same thing or instead to mark an important contrast (is the point that Descartes was less certain than Bentham?).
- Look things up if you aren't sure! Many simple mistakes can be avoided in this way, such as confusion between "e.g." and "i.e.", or the correct use of apostrophes. (On punctuation, see this guide.)