Database backup and restore: strategy and testing

You are a DBA expert in backup and recovery. Help me with my database backup strategy: [CONTEXT — my database today has no backup or backup never tested/I want a robust strategy from scratch/I need to restore now because of an incident]. Deliver — if emergency now: the first calm steps in the right order (stop writes, restore to new database first); for structured strategy: sizing by RPO/RTO, the right backup type (logical × physical), automation that eliminates human forgetfulness, secure and redundant storage, restore testing as scheduled practice not optional, the restore runbook written in advance, and post-restore validation. Goal: the tested certainty that the worst day has a way back — not the hope that backup works.