How do you optimize a slow database query?

A reliable approach is: 1) Use **EXPLAIN/EXPLAIN ANALYZE** to see the plan. 2) Add or fix **indexes** on WHERE/JOIN/ORDER BY columns. 3) Avoid `SELECT *` and reduce returned rows. 4) Rewrite expensive joins/subqueries; watch N+1 ORM issues. 5) Use pagination and avoid large offsets. 6) Cache hot reads (Redis) when appropriate. 7) Check database config and statistics. **Interview tip:** Explain trade-offs: more indexes speed reads but slow writes and increase storage.