Revisit your tiers at least once a quarter, so your sphere reflects the goals you're working on right now.
The idea
Treat your relationships like an investment portfolio. Nobody sensible trades their savings every day, and nobody sensible ignores them for a decade either. You rebalance periodically as your goals change. People's importance shifts, your priorities shift, and sometimes the whole structure of your sphere should change. Second-guessing your tiers weekly is unproductive. Once a quarter is about right.
How to do it
At least once a quarter, sit down and re-evaluate your setup.
Ask: do my goals still reflect what matters most to me?
Ask: does the way I've set up my tiers fit those goals?
Walk your top tier. Does each person still belong there? Who has earned a move up?
Expect to remove more people than you add.
Example
When I ran a consulting firm I was surrounded by talented people looking for work, but I wanted to stay a one-person shop, so I didn't track potential hires at all. Then I started Contactually and recruiting jumped to the top of my CEO to-do list, and talented people became my top tier. Once we had a recruiting team, that faded, and investors and executives at our biggest customers took the top spots. If my database in 2018 had looked the way it did in 2011, it would have been organized around a life I no longer had.
Watch out for
Don't day-trade. Moving people around every week is just anxiety with extra clicks.
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.
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.
The Review Cadence: Review weekly for 30 minutes, monthly for an hour, quarterly for half a day and yearly on a retreat, so you stop adding without removing.
Seasons of Your Network: Diagnose your season (planting, nurturing, harvesting or hibernating), match your effort to it, and give yourself permission to say no when it's winter.