Well, a basic idea of who each character is. A basic background and personality, maybe a couple notable features or quirks.
Your character I'm already familiar with since it's more or less the same character as in the last game.
You're all encouraged to come up with an interesting character hook (perhaps your character is a criminal and stole something from the wrong person, and they're out to find you; or perhaps you've been cursed and still haven't learned what the effect is; you may have found a strange egg, and some day it will hatch and reveal what sort of creature is inside; etc. etc.).
For instance:
A fighter who is captain of the Iron King's honor guard, as well as his daughter. Rather than fight with sword or hammer, she prefers heavy gauntlets, and her critical maneuver is Iron Barrage. On a crit, she pummels her enemies, tapping into the power of the Iron King (and taking on some of the visual and physical traits as a result, temporarily), making several extra attacks, on top of the normal bonus of a critical hit.
A warlock summoned from beyond the veil of this reality to aid the other adventurers, bidden by her Otherworldly Patron to finish the task or risk displeasing him. She was born with sight, but upon making contact with the patron entity, she was nearly driven insane by the unknowable presence but ended up merely losing her vision; she was repaid by her patron with the ability to sense without sight (blindsight). Her abilities are both eldritch and alien, and her critical maneuver is the Doom of Damaros. Darkness creeps upon the ground, from a wall, or above from thin air, and shadowy tendrils emerge to grasp the target. They are restrained, might be frightened, and if they don't escape soon thereafter, they are pulled into an alternate dimension.
A human monk abandoned at the monastery shortly after birth has never known his true heritage. He manifests a strange, arcane sigil, emblazoned on his body like a tattoo, and which grants strange powers over life and death. He discovers that his blood is mixed of both human and elven bloodlines, and he is the sole living heir to an ancient elven civilization long thought deceased. The only problem is that there exists another, unliving heir as well. As a Way of the Four Elements monk, he has powers over elemental forces, and takes on potent traits of the Elementals during his critical maneuver.
One of these characters is from the original Karthun source material, while the other two are characters in another game I'm running. It should give a good idea for the sort of hooks which might fit in with the campaign, and how their backstories and/or class shapes their critical maneuvers.