Static clues, specific information at a specific location attained in a specific way. Searching in the room will reveal a bloodstain. Flexible clues, specific information at a specific location that can be attained in multiple ways. You can get information from the target by threatening their family or persuading them. Proactive clues, Information that show up by themselves, usually in the form of an individual that can have more clues. The assassin was hired by John Doe, he must be the killer! Reactive clues, information found only by you coming up with a “unplannable” idea to look for. I cast divination to spy on the BBEG! Dynamic clues, information found in an unplanned way but that should logically provide it. Could be information that you just don’t know which skill will be used to find or it can be totally unplanned information by you but logically there should be a clue there. Investigator goes outside and look for tracks in the mud, it has been raining after all! Which not planned for but rationally sound as the escaping party ran outside. Unassigned clues, totally improvised clues based solely on improvisation based in a revelation list.
Define a revelation list that contains information that the group must know to make the adventure work and then determine which node/s should contain clues to lead to that each specific revelation and start adding them.
Avoid thinking which clues are in this smithy? but instead
prefer to formulate a more precise question like which clues in this smithy points to Fenurs magical hammer?.
Take inspiration from the groups different skills when creating clues to lean into something that they are good at.
Avoid having the plotter perform the perfect crime, plan or idea without holes. Fingerprints are left because of stress or recklessness and so on.
Just because YOU thought of a clue that the criminal would leave does NOT mean that the criminal thought of it and destroyed it.
When stumped to define clues, figure out ways that criminal made mistakes and add clues based on that. You WANT the criminal to leave clues to provide a trail of breadcrumbs.
Each clue pointing to a certain revelation should be found in a different way. Similar clues that are found in the same way are OK but count as a single clue in terms of The Three Clue Rule.
Clues should not be thought of as a puzzle and each individual clue should be able to lead somewhere. You should not need to collect x number of clues and puzzle them together to make them meaningful.
https://thealexandrian.net/wordpress/1118/roleplaying-games/three-clue-rule
https://thealexandrian.net/wordpress/40978/roleplaying-games/random-gm-tip-using-revelation-lists
https://thealexandrian.net/wordpress/46338/roleplaying-games/random-gm-tips-making-clues