Write the Queue, Not the Crowd
A crowd is a noun a lazy sentence reaches for. A queue is a data structure, and every person standing in one has a position, an arrival time, and a reason they have not yet left, three facts a crowd never gives you and a queue hands you for free.
Here is a sentence from an early draft of mine, a scene outside a clinic dispensing rationed antimalarial drugs after a shortage: "A crowd had gathered outside the clinic, restless and anxious, waiting for the doors to open." This sentence is not incorrect. It is also interchangeable with a crowd outside a bakery, a stadium, a bank run, because it describes a mood rather than a mechanism, and mood is the one thing a queue never actually has in the way this sentence claims. A queue has order, which is much more interesting than restlessness, because order creates unfairness the moment two people disagree about whose turn it is.
The queue method
Individuating a queue takes three moves, and I do them in this order every time. First, give it a length you could count, not an adjective: not a large crowd, but forty-one people, because a number lets a reader track scarcity as the line moves. Second, assign at least three positions in that number a specific person with a specific reason for being exactly there, not randomly distributed but placed by whatever rule actually governs queues, which is usually arrival time modified by who has been allowed to cut. Third, give the queue a limit, a point at which supply runs out relative to position, so that somewhere in your named forty-one there is a line, invisible to the queue itself, past which the drug simply will not reach them that day.
Rewritten with the method: "Forty-one people stood outside the clinic. Ngozi was eleventh, having arrived at five, ahead of anyone who did not sleep on the pavement the night before. The clinic had thirty doses. Ngozi did not know this yet. The man at position thirty-four did, because his cousin worked the dispensary window, and he had already decided not to say so." Nothing about mood was added. What changed is that the reader now knows exactly where the unfairness is going to land, and knows it before the characters do, which is the entire mechanism suspense runs on: information the reader has and a character does not, sitting inside a structure specific enough to be counted.
What this replaces
Crowd writing tends to lean on collective nouns doing collective feeling: the crowd murmured, the crowd surged, the crowd grew restless. Every one of these treats a queue as a single organism with one mood, which flattens the actual social fact of a queue, that it is a competition for position wearing the appearance of order. A queue murmurs the way a courtroom murmurs, which is to say each murmur is a different person calculating their own odds, and a reader who is given the calculation of even three of those people will supply the rest of the crowd's calculations without being told, because now they know the rule everyone in that line is running.
The obvious pushback
You could object that not every scene needs forty-one named positions worked out, that sometimes a crowd really is just a crowd, background weather for a character walking through it on the way to somewhere the actual scene lives. That is fair, and I do not individuate every queue a character passes. I reserve the method for any queue the plot returns to, or any queue where the outcome matters to more than one named character, the same threshold I use for the tariff sheet. A queue mentioned once in passing can stay a queue. A queue the story is going to resolve, where somebody gets the drug and somebody does not, has to be counted, because an unresolved crowd cannot produce an ending anyone can feel the shape of.
What happened to Ngozi
In the finished draft Ngozi gets dose twenty-nine, one place inside the line that mattered, and never learns how close she came to being the man at position thirty-four's cousin's problem instead of her own good fortune. The reader learns it, on her behalf, three paragraphs earlier, and that gap between what the reader knows and what Ngozi never finds out is worth more to the scene than every adjective I deleted to make room for it.