Before sorting anyone into A/B/C, name your goal and the types of people who help with it, so you know whose names to look for.
The idea
Prioritizing starts with the why. Most professional relationship work serves a handful of goals: generating new opportunities, keeping or repeating existing business, closing more deals, growing your network, building your brand. Each goal points to certain types of people, and those types point to names. Do this first and your tiers have a purpose. Then, within that pool, favor the people you genuinely like, because those are the ones you'll actually keep up with.
How to do it
Finish the sentence: "I'm investing in my relationships right now because ___." If the answer is "to build my network," push harder. A network for what?
For that goal, list the types of people who could help. A real estate agent chasing referrals might list former clients, lenders, and agents in other cities who send buyers her way.
Find the names that fit each type.
Sort those names A/B/C by gut, and spend the most time on the A's.
Quick win: pick five types of people for your main goal this year, and 50 people who fit them.
Example
At Contactually, our sales team had a party trick nobody wanted. We'd ask a new customer, "Why did you sign up?" People who answered "I want more referrals" or "I'm raising money for my company," we knew how to help. People who shrugged and said "I'm just trying to build my network" churned within weeks, like clockwork. For a long time I blamed our onboarding, or a confusing button somewhere (and OK, the software was occasionally broken). Eventually it was obvious: they had no why.
Watch out for
Your why will shift with the seasons. Mine went from investors to key hires to enterprise partnerships. Redo this when it changes.
Keep it to a few types. Elaborate bucket systems are how people burn out.
Start With Why - Set Your Relationship Goals: Before building any system, decide what you want from your relationships and why. Opportunities, retention, referrals, a brand, or simply feeling good.
A/B/C Spheres: Sort everyone into three tiers by gut feeling (love, like, don't know) and spend more time on A's than B's, and more on B's than C's.
CAPITAL: Prioritize: The P in CAPITAL - decide who matters most right now and focus there, because you can't give everyone in your database equal time.
The Tuesday Test: Finish "I'm investing in my relationships because ___." If that answer wouldn't get you to send a message on a busy Tuesday, it's a should.