This brief article is titled "Backing up for Mortals," and it looks like it has good advice. The author recommends 3-2-1 Rule:
The rule is simple: you have 3 backup sources: 2 are local, and 1 is remote.
2 local sources because if one fails, you can replace it and duplicate the good one over the new one.
1 remote source because if both fail, or become destroyed or stolen, your remote source can restore 2 new local sources.
The two local drives should be mirrored — "A mirrored drive is best for backups because if any data becomes corrupt in one, the other can restore it; it's maximum redundancy."
The author recommends using Backblaze, which costs $60 a year and offers unlimited storage. I'm using IDrive, which costs $70 a year and it's limited to 5 terabytes of storage, but you can back up an unlimited number of computers, so I have the whole family backing up their computers to it.
The author also recommends encrypting backups on a file-by-file basis "(if data becomes corrupted, it's hard to recover anything without a copy"), but that seems like too much trouble for me, so I am just in encrypting everything and crossing my fingers.