No worries :} My rule of thumb for things like discern realities and spout lore, is that they sneak up on you. I think they come about most often when you push your players for more detail.
You enter a small dingy room with a hallway continuing straight ahead, and a small, shabby door on the right-hand wall. What do you do? Do you keep going down the hall, open the door, or lay out a picnic?
We should open the door, right? Make sure there's nothing cool in there. I'll head through the door.
You're a thief, right? Are you just going through like you're entering a shop?
Ah, right, no. I'll go slow and check for anything that looks dangerous or trappy.
Discern Realities it is!
For Spout Lore, I would lean on something you already do and ask if they know about a topic, or if they studied something, and if they say yes, then have them roll. Remind players early in the session, too, that if they are feeling stuck then Spout Lore is a good way to close the gap where the character knows something the player doesn't.
When the group was trying to figure out what was happening with the nasty bugs you might have asked Eli if he thought he might know about creatures like these bugs, or if they're beyond his experience.
Spout Lore gives you something interesting, and possibly useful, but never vital. Same with Discern Realities. If the door is trapped the players will find it out, but if the person they're chasing went through the door and it wouldn't be fun to have them traipse around hallways for several in-game hours, then it's totally fine to mention that the dust is smudged near the door. That's probably enough to let them know that they should search and trigger the move.
For sneak attacks I like to pick one person based on whim, fictional positioning, or lack of spotlight and tell them that they see the thing starting to happen to another player and what do they do!? Zey's about to step on a very obvious trap, Nyx, what do you do? A giant grasshopper is falling toward Ventuz, Alaebas, what do you do? Or even have them notice it themselves. Ventuz, there's a fairly huge praying mantis-type monster inches from biting into the back of your skull. Did you want to do anything about that?
Anyway, love the show, love your games, love hypotheticals :} I need to send in an email for you and Tappy.