I have a copy of the Hávamál, which is a collection of 1,000 year-old poems translated as 'Sayings of the Vikings'. I found useful when I was writing my Norse stories Daughter of Fire and Ice and Sigrun's Secret as well as more recent younger stories.
It wasn't that I used anything from it directly in my writing. It was more that it gave me a sense of how the lives of the ancient Norse people were different to ours and also in which ways they were similar.
One of the ways their lives were very different was danger; especially danger of violent death. Thinking of Iceland, for example, as that is the Norse culture I'm most familiar with, there were clear laws and those who broke them could be sentenced to outlawry or fines. But there was no law enforcement, so if the guilty party failed to comply, his enemies would take matters into their own hands. Moreover, Viking tempers were quick and their sense of honour was strong, so feuds frequently arose.
Thus the Hávamál has a few warnings for observing personal safety:
Advice to a Vistor:
watch as you walk on,
inspect as you enter.
It is uncertain
where enemies lurk,
or crouch in a dark corner.
Famously, assassins would climb up in the roof space of doorways and drop down on unwary victims, killing them before they knew what had happened.
This gives such a flavour of the era. It is impossible to imagine in our lives today (in Europe anyway) having to inspect a doorway before walking in.
There are also warnings on quarrelling at feasts as feuds can follow and on guarding your tongue and carrying weapons when you leave home.
Then there are the sayings that are as useful today as they were in the days of longhouses and battle axes:
When to keep silent
Often it's best
for the unwise man
to sit in silence.
unless he tells too much.
It's the ill-fortune of unwise men
that they cannot keep silent.
There are plenty of warnings, too, about alcohol: "drink is a dangerous friend," and "ale unveils [the] mind." There is no doubt that foolish behaviour after drinking is a thousand-year-old issue at least.
Highly recommended for some insight into manners and etiquette of the times!