Xayah Runes explained
There's one set of runes for Xayah on patch
11.8
that is the clear favorite for LoL players and pros alike. The best Xayah Runes on the position 
Adc are Precision as the primary path and
Inspiration as the secondary path with a pick rate of 68%. Besides runes you should take a look on Xayah Build and if you are interested in pro matches take a look at Xayah Probuilds. If you want to discuss
Xayah then you should visit the champion subreddit.
Primary path on Xayah
Precision improves attack and sustained damage on Xayah troughout the match. Most of high elo players – and our LoL pros in the the major regions – have agreed that
Lethal Tempo is the best keystone rune to run on
Xayah. This keystone rune gives Xayah a great head start in team fights and allows to put out more damage in that time window. This is usually followed up by taking
Presence of Mind,
Legend: Bloodline and
Cut Down.
Presence of Mind helps Xayah with the mana problems by restoring missing mana, if a champion is killed.
Legend: Bloodline gives life steal, which aids in winning damage trades and fights in the later stages of the match. If the enemy team consists of multiple tanks, then the rune
Cut Down is the best choice.
Secondary path on Xayah
When it comes to your secondary path, most
Xayah players prefer to go with
Inspiration.
Inspiration opens creative opportunities on Xayah troughout the match. On the
Inspiration path, the best runes for Xayah are
Biscuit Delivery and
Cosmic Insight.
Biscuit Delivery is a great rune for laning as it gives additional health and mana, which can help in more aggressive lanes.
Cosmic Insight grants summoner spell and item haste.