There's nothing complicated about company culture.
Culture simply happens. It's emergent behavior. There's nothing to do, it just is.
A company's culture is a 50-day moving average. It's what you've been collectively doing as a company over the last 50 days.
How do you treat people? Who have you hired (or fired) and why? What do you when people are stressed out? How do you help people? How do you critique each other? How do you share? How do you help people who are stuck? Where's the bar on quality? How do you support customers? How do you close deals? What have you let go on too long? What have you celebrated? What have you let slide? How honest have you been with each other and yourself.
It's all that and a zillion other things. But it's all stuff that actually happened, it's not lists of things you wish had happened, or declared would happen in some ideal setting. Much of it is interpersonal, expressed both inside and outside the organization.
Why 50 days? It's enough time for patterns to emerge, yet malleable enough to be current and honest. One day, or even a couple weeks, isn't enough to stand for culture. A series of moments tied together loosely by near-term time just isn't enough to establish what it's really like somewhere. We can all be on our best behavior for a little while, but the longer while tells the truth.
Culture is the non-fiction story of an organization. It writes itself.