Considering several sources and my own experience running and playing games on the OSR Pick-Up Games Discord server for the last two years, I have created a list of the (currently) eight mantras of OSR-style gaming I most frequently hear and repeat:
1. Imagine the Hell out of it.
2. The OSR is rulings not rules.
3. Play worlds not rules.
4. The OSR is a mindset, not a rules set.
5. The OSR is problems without prescribed solutions.
6. The answer isn't on the character sheet.
7. Combat is a fail state. (I dislike this one. It's become dogma.)
8. The OSR is the players' story, not the game master's.
Here's to another year of OSR gaming!
— Stripe