Second-year philosophy student at a mid-sized Canadian university. I don't think I am in any place to give advice that should be valued over that which is given from graduate students, teaching assistants, professors, etc. But I have (somehow...) yet to get below an A- on a philosophy essay thus far in my schooling, and I think one thing that really, really has helped me is: (a) clarity in the introduction, and (b) a good method of organization.
More particularly, I find that signposting helps, as well as headings and directions.
For example, starting papers off, or at least having one of the first sentences of this paper be:
"The intention of this paper is to..." "This essays seeks to contribute to an understanding of...." "This paper proceeds in five parts. Part one attempts to reconstruct X Y Z theory... Part two proposes that...." etc. I think having a clear objective and letting your reader know what exactly it is that you are discussing at all time really helps!
But, the caveat of course is that I am a mere student and can be totally wrong about this - anyone, feel free to correct me if necessary.
As for headings, this may just be a stylistic thing, but it helps me personally to organize my thoughts, and it reminds my reader what topic I'm exploring in a certain paragraph (or series of paragraphs). Especially for essays that are more convoluted and difficult by nature.
For example, one thing that helps me is to proceed as so:
Section I. Reconstructing Nozick's Argument
[...... Fill in paragraph here]
Section II. Objections to the Entitlement Theory of Justice
[.....]
And so forth.
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Also, some helpful guides: https://philosophy.fas.harvard.edu/files/phildept/files/brief_guide_to_writing_philosophy_paper.pdf
http://philosophy.fas.harvard.edu/files/phildept/files/guide_to_philosophical_writing.pdf