Beyond business-relevant contacts, make sure your network includes a professional contrarian, an industry oracle and a universal connector.
The idea
Your primary filter for proactive attention should still be business relevance or personal affinity. On top of that sits a secondary layer most people miss: roles that are just helpful to always have around.
The Professional Contrarian red-teams everything you say. Exhausting, which is exactly why most people avoid them and why you need one. They poke holes in your thinking before the market does. Find one who disagrees constructively and respects your goals.
The Industry Oracle always seems to know what's happening and what's coming next. Rarely the most famous person; often in an adjacent industry or specialized role with a unique vantage point.
The Universal Connector always knows someone: three website designers, the right lawyer, the person with that exact set of skills. One good connector is like a relationship with dozens of specialists.
How to do it
Look through your current relationships. Do you already have someone in each role?
If not, start noticing the qualities in people you meet. The contrarian might be the colleague who plays devil's advocate in meetings. The oracle might be at a trade publication or industry association. The connector is the person who somehow knows everyone at conferences (consultants and journalists often are).
Example
These days my own "why" for staying in touch is exactly this: nurturing a kitchen cabinet of people I can tap for advice, ideas and inspiration, who expand my thinking. If you already have all three, congrats - you're basically running the Justice League of business.
Your Network Is Your North Star: The people around you expand or shrink what you believe is possible, at work and at home, so choose them on purpose and keep a small growth circle close.
The Little Black Book: Keep a running list of promising people early in their careers and get in their corner before everyone else wants a piece of them.
Three Connector Personalities: Conveners build dense networks, Brokers bridge worlds, Expansionists cast wide nets; find your natural style and lean into it.
Depth by Default: The people you already know already trust you, so deepen first; expand only for a specific reason, and follow up with two known people for every new one.