What's the most effective way to create a strong team culture?

Be a servant leader. Treat people as people first, and not a means to an end. Trust your team.

Squash any sign of passive aggressiveness and your 90% there. And create a mentor / mentee culture.

I think it starts with leadership. The top of the ladder needs to show interest in helping the other teammates meet and exceed their goals, in work and in life. You spend more time with the people you work with then you do your own family, so making sure everyone is in an environment where they feel wanted, safe, and can trust their peers, the culture and business will thrive.