Placing arcana
Be thoughtful about how often you introduce new arcana. Between unlocking them, using them, and dealing with their consequences, they can have a huge impact on the game. Give the players too many and they'll be overwhelmed with options. Give them too few, and you'll be missing out on a fun part of Stonetop. Don't be stingy with arcana, but don't hand them out like candy, either!
Most arcana are artifacts; place them as such. Try to place them in a way that implies a story or at least illuminates part of the setting.
Caradoc and Vahid take a short trip to the Ruined Tower in early autumn, to poke around and see what they find. Caradoc spends a few hours scouting out the outer ruins, Seeking Insight. He asks, "What here is useful or valuable to me?"
The Ruined Tower entry in Book II includes a number of discovery tables for the outer ruins, including one for "something valuable." I roll and get "a half-buried plaque, or some other artifact of the Tempest Lords." The halfburied plaque seems like a perfect thing to find in the blasted rubble around the Tower.
.
I pause to consider whether I want to add this arcanum to the game. It's right up Vahid's alley, and while he has a few stilllocked arcana, he can't easily act on them just yet (one requires that he suffer a terrible burn; another needs Rhianna's help and she's busy; the third involves finding pieces of the Mindgem's body and he has no leads.) This is an arcanum he could act on now, and one that I think would be fun to see in play.
"Okay," I tell Caradoc, "In the rubble near the tower, you find this bronze plate poking out of the soil…"
Some arcana are sites, or part of one. Place them where they make sense, and feel free to tweak the details on the front of the card. The "runes around a ruined hall" arcanum describes a throne room, but maybe a smithy makes more sense in your game?
A few arcana represent tales or specific encounters. Present these to the PCs as clues), encounters, or opportunities. Again, feel free to modify the specifics on the front of the card to meet your needs.
A handful of arcana—notably Storm Markings and the Ineffable Words—represent a PC being infused with magical power. Offer these as opportunities, or even inflict them as consequences when the PCs are exposed to truly potent magic.