Start with the candidate set
A catalog can contain more items than a product experience can show. Candidate retrieval narrows that catalog to a useful set. Content similarity, collaborative signals, popularity, and semantic retrieval can each contribute, depending on the available data.
Rank for the actual context
Ranking scores and orders the candidates for a particular user, session, or placement. Recent actions and catalog attributes can matter alongside historical interests. Re-ranking can also work on results returned by an existing search system.
Apply constraints deliberately
Availability, eligibility, diversity, and duplicate suppression are distinct from a learned relevance score. Make those constraints explicit so a technically relevant result still fits the product experience.
Evaluate the whole journey
A ranking change should be assessed against a defined objective and guardrails. Item coverage and segment behavior can add context to aggregate engagement. Choose a baseline before interpreting improvement.