Be friendly and respectful towards others and third parties. Treat others the way you yourself want to be treated.
Be considerate. Not everyone shares the same viewpoint and priorities as you do. Different opinions and interpretations help the project. Looking at issues from a different perspective assists development.
Do not assume malice for things that can be attributed to incompetence. Even if it is malice, it’s rarely good to start with that as initial assumption.
Stay friendly even if someone acts contrarily. Everyone has a bad day once in a while. If you yourself have a bad day or are angry then try to take a break and reply once you are calm and without anger if you have to.
Try to help other team members and cooperate if you can.
The goal of software development is to create technical excellence, not for any individual to be better and “win” against the others. Large software projects are only possible and successful through teamwork.
If someone struggles do not put them down. Give them a helping hand instead and point them in the right direction.
Finally, keep in mind the immortal words of Bill and Ted, “Be excellent to each other.”