1. Daily backup. Personal documents take up one directory tree amongst the many directory trees of my /home/username directory which is backed up in full every day. Those daily backups are discarded in a reverse-exponential way, such that there many recent backups and fewer older backups.
Those daily backups are duplicated twice more on to two separate external hard drives.
2. Monthly backups, documents only. The whole of my documents directory tree is tarred and compressed as a monthly 'snapshot' and this is stored as three separate instances on three separate hard drives, one internal and two external. Those monthly backups are stored indefinitely and never discarded.
NOTE: I know I should have another copy stored off-site as 'belt and braces', but I know from painful experience that 'cloud storage' can be less dependable than a home-grown solution. And the triple-copy on-site system has served me well so far.