For each person, know three things - how you know them, how you feel about them, and when you last talked. Everything else is optional.
The idea
In my coaching we boiled the whole database down to three questions per person. How do I know them? How do I feel about them? When did we last talk? How you know someone sets their group, so you don't treat a past client like a vendor. How you feel about them matters most, because it moves the question from what they can do for me to how I feel about them. Last contact catches the drift. Missed opportunities come from two places: going quiet too long, or sending generic blasts instead of connecting, while someone else earns their trust.
How to do it
Group each person by how you know them: client, past client, personal sphere, prospect, vendor or partner, peer.
Tag how you feel, fast: love, like, or don't know (A, B, C).
Make sure something tracks your last contact and tells you when it's been too long.
Keep it simple. You can get more complex later, once the basic habit of organizing is down.
Example
Say you open a name in your phone. You know her from a past project, so she's a past client. You light up when you see her name, so she's an A. You last talked in March, and it's November. Those three answers already tell you what to do: she's overdue, you love working with her, and you have a shared history to reference. Send something human today.
Watch out for
Tagging by who you think could send business. You don't really know, and the people you love are the likeliest to anyway.
Groups vs. Tags: Put each person in one group by how you know them (client, past client, sphere, prospect, vendor, peer) and use tags for everything else.
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.
Contact vs. Relationship: A contact is a name and an email; a relationship is the history, context and personal knowledge, and that's the part with value.