the game is much more flat with just one player, so I would recommend a couple things. First of all, consider dropping highlighted stats entirely, and embrace the whenever you fail a roll mark an experience alternative. Then focus your attention as the MC into really bringing to life other npcs and the atmosphere of the narrative. It is often good to start them off running, as in with an immediate goal in a tense situation. Movement becomes one of the most important parts of keeping the story interesting.
Additionally, you will want to keep in mind that you're essentially MCing at the intersection between the characters brain and the world. So you can essentially move into the psychological pretty easily, messing with perception, truth, meaning, and reality itself. I found some horror genre's play extremely well with one character in this regard, because they cant look to the guy next to them and say.. did you see that?