Every guide on this site depends on other people having written useful reviews. Most reviews aren't. "Great food, great service, will be back!" helps nobody, and that's the majority of what's out there.
Writing a good one takes about ninety seconds.
This is the whole trick. Specifics are what make a review useful, and vagueness is what makes one worthless.
Say what you ordered. Say what time you went. Say how long you waited. "The carnitas tacos were excellent, the fish ones were dry" tells the next person what to order. "Food was good" tells them nothing they couldn't have guessed from the rating.
The test: could this sentence be copied onto a different business's page without anyone noticing? If yes, it's not doing any work.
Mention at least one specific thing by name. Everything else is optional.
A restaurant that's wrong for one occasion is perfect for another. Telling people which situation you were in makes your review usable by people in different ones.
"Too loud for a conversation but great for a group" is genuinely more helpful than four stars with no context. So is "we had a toddler with us and nobody minded," or "went alone and sat at the bar, which was comfortable."
Nobody thinks to write these and everybody wants to know them:
A single sentence covering two of these makes your review more useful than three paragraphs of adjectives.
This is where reviews do the most damage or the most good, so it's worth being deliberate.
Say what happened, factually. "Our order took 50 minutes and arrived cold" is far more useful — and far more damaging to a business that deserves it — than "terrible service, avoid."
Say whether you gave them a chance to fix it. This is the single most valuable thing in a negative review. "I mentioned it and they remade it immediately" and "I mentioned it and was ignored" describe completely different businesses.
Consider whether it's a pattern or a bad night. Everyone has an off day. One slow evening at an otherwise good restaurant probably isn't a one-star situation, and rating it that way makes the whole system less useful for everyone.
Don't review things that aren't theirs. The weather, other customers, traffic, a delivery app's failure. It drags down a rating for something the business couldn't control.
Barely anyone does this, and it's the highest-value thing available. If a business fixed your problem, went downhill, or you've been back ten times since, edit what you wrote.
A review that says "updating a year later — still consistently good" is worth ten fresh five-star reviews, because it's evidence over time rather than a single moment.
Worth knowing: it's now illegal in the US to write a review for a business you have no experience with, or to be paid for a positive one. If a business offers you a discount in exchange for a review, that's a violation on their end.