Tag by intent, not by title
Tags like "Marketing" tell you what someone does. Tags like "Potential customer", "Hiring pipeline" or "Introduced me to people" tell you why they are in your list, which is what you actually search on.
Job titles change. Your reason for knowing someone rarely does.
Always record where you met
It is the most reliable retrieval key you have. People remember contexts far better than names — you will recall "the woman from the Bangalore summit" long after her name has gone.
One field, filled in at capture, makes your whole list searchable by memory rather than by spelling.
One note per interaction
Do not maintain a single growing blob of text per person. Separate, dated notes let you reconstruct a relationship in order and see where the gaps are.
This is also what makes a relationship timeline useful rather than decorative.
Prune, but do not delete
Contacts that have gone cold are not worthless; they are dormant. Archive rather than delete, because the person who was irrelevant last year may be exactly who you need next quarter.