Fred Brooks, in The Mythical Man-Month, hit the key principle that always guides me:

Show me your (code design) but hide your data structures,
  and I will remain as ignorant as before.
But show me your data structures,
  and I won't need your (code design); it will be obvious.

Or as Deep Throat might have said: "Follow the data."

    -- Chip Salzenberg, Free-Floating Agent of Chaos