Ask HN: How do you create high quality professional relationships?

I'm interested in hearing how the HN community builds and maintains strong professional relationships that last for decades.

In my career so far, I've really valued having a diverse network of colleagues, mentors, and friends across different disciplines and companies. It's been invaluable being able to reach out to my network for advice, feedback, referrals, and even just catching up. I work as a data scientist but try to always meet and connect with at least 4 people at my companies in non-DS roles.

Some questions for the HN community:

    How do you intentionally build your professional network over the years? Do you stay in touch with all co-workers or be selective?
    What are your tips for maintaining meaningful relationships once you no longer work at the same company? How often do you connect?
    Who have been your most valuable mentors and how did those relationships form? What made them high quality?
    How have you helped colleagues over the years and how has that benefited you in return?
    What platforms or mediums do you find most effective for staying in touch? LinkedIn, email, phone calls, conferences, etc?
    For early career folks, any tips on how to start building a network and relationships that will last throughout your career?

I've found having a broad professional network invaluable over the years, so I'd love to hear how others think about this. What has worked well for you in creating high-quality, long-lasting professional relationships?