This is a set of general tips and general backup strategy.

Have two disks

This is the first and most important advice.
You never know when the disk may fail.
Have another exact copy on different hardware, with different file system
at different physically place.

Perhaps you should also use smartmontools to check disk health.

Get reliable fast disk

Do not use flash drives and SD cards as a primary storage.
There is no warranty of redundancy and many manufacturers lie the specs.
It can be painfully slow to copy and even slower to write.
It may stop working.

SDDs are good for raw speed, however these are not supposed to live long
without electricity supply and may become unreadable and unrecoverable after
few months on shelf.

HDDs are top recommendation for cost efficiency and reliability.

Use reliable file system

ZFS or Btrfs file systems are self-repairing and recommended.

Most disks come preformatted FAT32, EXFAT or NTFS,
do not use these file systems. These only have basic
protection against write errors and may be exposed to bit rot.
EXT4 and XFS are better but may suffer from improper unmounting.
Once again: use btrfs.

Separate images by source

If you have more than one camera, e.g. both phone and photo camera,
I strongly recommend to keep images from each device in a dedicated project copy
and dedicated library. It is then much fancier to view images.

This is especially true if you want to track raw images (see below).

Index RAW files separately

These are far not easy to view, they take more space and not always necessary.
You should set up another library directory and change the home/symlinks.py header
to accept your raw photo format (and nothing else).
Interactive review may not work for them depending on format.

Do not produce large images

If your camera produces high resolution images (>16MP),
Consider to set smaller image size. Do not be aware
of older cameras, consider better lens instead.
Reasoning: large images exceed the capacity of absolutely
most screens and practically never printed in full resolution.
Smaller images well fit on optical media and more easily shared.

backup symlinks

While it may seem to be harmless to remove few symlinks,
I swear you don't want to get lost all symlinks collection.
It carries information of all correct file groups!

Keep tarballs

Either you share images or download from someone,
signed tarballs are convenient way to transfer files.
It also faster to move between local disks and ensures integrity.
Do not remove downloaded tarballs but save them to archive instead.
Archived files should be set read-only and carefully backed up.

Burn (dvd+-r) optical disks

These can survive fatal programming mistake and catastrophic disk failures.
Despite not exactly cheap, this is actually recommended.