Conspiracy theories follow four moves.
The moves are independent. You can apply them to any news story, real conspiracy, or made-up event. Once you can name them, you can spot them. The recipe is set out at length in this blog post, with the academic version at this paper.
Hunt anomalies
Turn coincidence into evidence of a secret plot.
Look for puzzling details or contradictions in the official story. Insist they prove the official story is false. You're "just asking questions" — and since no explanation of any event is ever complete, this part is easy.
The tell. Real investigators look for patterns that survive a base-rate check. Conspiracists collect anomalies and forget to ask how often a coincidence of that kind happens by chance.
Fabricate connections
Draw lines between unrelated dots until they look meaningful.
Fabricate "evidence" that implicates your culprit. Forge suspicious connections between the official story and your culprits — the tighter the network looks, the better.
The tell. "Six degrees of separation" works for any two people on the planet. Treating a six-link chain as evidence is a category error: the connection exists in every direction, not only the one being highlighted.
Dismiss counter-evidence
If a fact disagrees, make the fact part of the cover-up.
Argue that any disconfirming evidence is missing because the conspirators covered their tracks — and any apparent counter-evidence was planted to throw truth-seekers off.
The tell. When counter-evidence becomes further evidence of the conspiracy, the theory has become unfalsifiable. Any disconfirmation just expands the circle of conspirators.
Discredit the critics
Dismiss people who point out flaws in your theory.
Critics can be dismissed in different ways: they're gullible dupes, they've been manipulated, or they're paid stooges of the conspirators themselves.
The tell. Ad hominem framing reroutes the question from "is this true?" to "who is asking?" Real investigators welcome critique; conspiracists treat it as more evidence of the conspiracy.