I'm just fan of Xayah and i'd like to show to you my runes/builds.
I'm adc/support main, who use personal runes.

Firstly I'd choose the precision tree, from which i'd take Conqueror because it's give a lot of damage in mid/late game. You can easily stack this rune, but hard to use it. If you can use this rune with your W and E then you can deal a lot of damage immediately. I tried Flootwork, but it doesn't works well in late i guess and i lethal temp work well in early-mid game too because in late game you will have enough attackspeed from W and items. Press the attack well, i think it doesn't works well because you have to hit one enemy 3 times and then it give bonus damage as long as conqueror give TRUE DAMAGE.

My next choose is triump because it's gives extra survivability in lane if you get a kill and extre gold.

After triump i would choose Legend:Alacrity for extra attack speed because i don't have extra attackspeed from lethal in early because i use conqueror or the other choice is Legend: Bloodline but i never felt this rune usefull especially in early.

Lastly i'd take Coup de Grace for the usual stuff. Gives you more damage as you burst down enemies.

In second tree i pick Sorcery. First rune you take is Celerity because it's very usefull. It's give a bit damage but the main reason because i choose it the bonus movementspeed what make easier to beat the distances.

Second rune is Gathering Storm. It's help to scale better and even if you have bad laning, then this rune help you in scaling.

You don't need Lord Dominik's Regards or Mortal Reminder because of Conqueror what give you much true damage.
You have to take Mortal reminder only when enemy have soraka or mundo or someone who have strong heal regen/steal.

Clean Cuts
After using an ability, Xayah's next few basic attacks will hit all enemies along their path and dropping Feathers she can recall.

Double Daggers
ACTIVE: Xayah throws two feather-blades in quick succession, dealing physical damage, and leaving two Feathers on the ground.
Targets hit after the first take 50% damage.

Deadly Plumage
ACTIVE: Xayah creates a storm of blades for 4 seconds that grant her attack speed and cause her basic attacks to strike an additional time for 20% damage.
If Deadly Plumage strikes an enemy champion, Xayah gains 30% movement speed for 1.5 seconds.
If RakanSquare Rakan is nearby he will also gain the effects of Deadly Plumage.

Bladecaller
ACTIVE: Xayah calls all Feathers back to her, dealing physical damage to enemies, and the total damage is halved against minions.
Enemies hit by at least 3 Feathers are Root icon rooted for 1 second.

Featherstorm
ACTIVE: Xayah leaps into the air becoming untargetable for 1.5 seconds, during which is still able to move, then rains down daggers which deal physical damage and leave behind a line of 5 Feathers.