Cleanliness. In other words, general consideration for each other's space. A good rule of thumb is to talk about what kind of messes stress each other out and figure out a way to compromise. This doesn't necessarily mean you need to make your bed every single day, but do learn what cleaning habits bring peace to your roommate's life and do them joyfully!
6. Respect. This is so huge. Mutual respect for each other will bring much peace and less eggshells into your roommate-ship. Try your best to show your roommate that you respect them, rather than just telling them. Respect their sleep by quietly coming into the room at night. Respect their time by cleaning up your mess so they don't have to. Respect their space by giving them the freedom to be themselves.