Well just to stick to one example, with call of cthulhu, a couple things like
"There are Obvious Clues and Obscured Clues. Make sure Obvious clues are not something the players need to work for Especially if missing that clue make them stuck. Obscured Clues should be helpful but not pivotal to the investigation."
"Try not to lead your players when describing evidence. You should describe to them how the players found the evidence, not how they would feel or think about the evidence. Leave it up to the players to make their own deductions."
"The players can be creative when looking for leads in an investigation. Try to incorporate that creativity and let leads manifest when it makes sense for it to do so."
"While most perception checks are to look for Clues, you should ask your players if they might have a different goal in mind such as looking for a journal with relavant information. If you are happy with that goal, let them roll perception to find it. If not modify the goal to something more appropriate or use normal rules for looking for evidence where there is none."
"When the players seem stuck or bored then its time to give them a nudge. Introduce new information or dramatic moment. Maybe an NPC calls for aid with a problem that is relevant to the investigation."
"If your players are completely stuck offer them an idea roll(a hint roll). If a character succeeds they make an important connection with their current investigation."
"A failed roll doesn't necessarily mean the goal fails. If failure would lead to a stop in play consider alternates. Such as if an investigator failed to open a locked door in a flooding room, rather than the investigators all drown and end the session, have the failure be the investigator opened the door at the last minute causing great damage to the group as the full room of water pushes and crashes them into the next room. The goal of opening the door was achieved but at great cost to the group for the failure."
All paraphrased.
I'm not saying this stuff is super special advice that you can only learn from call of cthulhu. Or that all these lessons are useful for every game type. I'm sure that most experienced DMs will figure this stuff out and what works for them eventually.
However, if you were like me and didn't know anything about mystery pacing and placing the right clues from previous rulebooks and gaming, these ideas greatly improved my mystery design by giving me written rules/ideas to think about and experiment with. Most importantly it gave me a load more direct and tangible experience with this concept. I was actually doing a mystery every session with call of cthullu rather than a few sessions out of a year with dnd.
