The structure of the project. How are decisions taken? What's the legal framework? What are conditions put on usage and contributions?
The following stepping stones form the path of governance. They are not in a specific order. Each project will pick and arrange them in a way that is suitable to them.
Independent non-profit foundations are a good neutral ground to represent and protect a project and allow others to collaborate as peers.
Limiting influence of single companies is a good practice, e.g. by preventing a majority of a single company in board decisions.
Use an umbrella organization unless you have a very good reason to run your own one.
The license has an influence on culture and practicalities. Choose wisely.
The trademark is one of most valuable assets of a successful open source community. Have a policy which defines how it can be used.
Transparency about how to contribute is one of the most essential pieces of empowering people to contribute.
Avoid a CLA, this creates barriers. Use a DCO if you want something more explicit than what a license gives you as well.
Keep your partners close. Sometimes a formal partnership can open doors and help in discovering and using common opportunities.
Make it clear what expected behavior is in your community and provide a path for acting on violations.
Make explicit what your culture is. Write it down. This helps new people to understand and everybody to remember. It also can trigger a discussion about what actually is important. It also can be a foundation for defining procedures how you want work in your project.