The 5-paragraph structure as a starting point
The classic five-paragraph essay - intro with a thesis, three body paragraphs, a conclusion - exists because it's a reliable container for a simple argument. The intro sets up your thesis, each body paragraph proves one piece of it with evidence, and the conclusion ties everything back together without just repeating the intro word for word. Once you're writing longer pieces or juggling more than three supporting points, expand beyond it: add more body paragraphs, or group related points under sub-sections. The structure is a scaffold, not a rule.
A clear thesis statement
Your thesis is the one sentence a reader could point to and say "that's what this essay is arguing." It should be specific enough that someone could disagree with it - "social media affects teenagers" is too vague to argue; "social media use before bed measurably reduces teen sleep quality" gives you something to prove. Write your thesis first as a draft, then revisit it after you've written the body, since your argument often sharpens as you write.
Hitting a word count without padding
The wrong way to add length is repeating the same point in different words. The right way is going deeper: add a specific example, quote a source and explain why it matters, address a counterargument, or explain the "so what" behind a claim you made too quickly. A paragraph that says one thing three times is weaker than a paragraph that says one thing once and then proves it. If you're short on words, that's usually a sign you need more evidence, not more sentences.
Topic sentences that connect back to the thesis
Every body paragraph needs an opening sentence that does two jobs: state what this paragraph is about, and show how it supports the thesis. A reader skimming just your topic sentences should be able to follow your entire argument. If a topic sentence could get dropped into a different essay without anyone noticing, it's too generic - tie it explicitly back to your specific claim.
Self-editing techniques
Read your essay out loud - your ear catches awkward phrasing and run-on sentences that your eyes skim past. Cut words that aren't doing work: "very," "really," "in order to," "the fact that" can almost always be deleted or shortened without losing meaning. Search for words you overuse (most writers have two or three) and swap in variety, or better, cut the sentence down instead of finding a synonym.
Editing vs. proofreading
Editing happens first and deals with the big picture: does the argument make sense, is the evidence in the right order, does each paragraph earn its place? Proofreading comes last and catches surface errors: typos, punctuation, formatting, citation style. Doing them in the wrong order wastes time - there's no point fixing commas in a paragraph you're about to cut. Leave real time between finishing a draft and editing it; even a few hours of distance makes problems easier to spot, since you'll read what you actually wrote instead of what you meant to write.
Putting it together
None of this needs to happen in order on the first try. Plenty of strong essays start as a rough thesis and a list of evidence, get reorganized into paragraphs once the argument is clear, and only then get trimmed and polished. What separates a strong essay from a weak one usually isn't talent, it's whether the writer went back and cut what wasn't earning its place.