They should probably play Ascension. Koth of the Hammer is pretty good too. You could do both—why didn't we think of that?
Do something unfair. It's a one-for-one deck so if you're just out-carding them in unfair ways . . .
You can't be very linear—you have to have versatile attacks and you have to be resilient. Hand disruption mana disruption or countermagic will keep them from getting Jace and stabilizing.
Know how to play against it—the deck's not that hard to beat and you need to kill their Jaces. If they get one Jace with a foothold the deck gains so much incremental advantage. Attack their Jaces even if you think they have multiples.
If I knew the answer to that I would probably do better in this tournament!