Full Walkthrough:
Sheldon, Zane and Sammy are pretty straightforward. Just choose the option that will cause you to meet them during break time and that's it. It doesn't matter if you mess up or do all their orders properly or not.
For Creator and Game Interface Route, you need to get all orders right, select 'Say nothing' when you sit with Sheldon, and then when you reach the end with the three buttons that say 'Return to start', click on the middle one, and you can access the secret routes.
For Grace, you have to get only the first order right, and mess up the others, and then select 'Say nothing' when you sit with Sheldon. Ask her to be your girlfriend for her ending, and if you choose 'Friend' you get a hint for the 'POV character ending'.
For the 'POV character' route, just name your character after the name Grace mentions in her 'Friend' ending.