Welcome to my first Build here!

Because of my bad english i have to keep this very short!

+ when played defensive you can hit a perfect Score ( 10 / 0 / X )
+ Ultrarange
+ fun to play
+ good farmer
+ Variable to play (mid or lane)
+ tanky vs mele]
+ Action all the time
+ Items are not sooooo important [/color

- squishy vs mage
- hard to play the first couple of times
- dead when u got silenced or stunned

I reccoment Flash. You just need it to flee. You can also take Clairvoyan instead of Flash to see where the low-healthy Enemy is going to flee, so you can get him with your W, Q Combo.

For the second Spell i take Clarity. Especially in the early game, your Mana is always low. Its defenetly the best Spell to choose for Xerath.

The key to be successfull with Xerath is to know how to use his Combo:

Until you reach lvl 6:

W -> E -> Q -> W and then fall back.
You already can cast E after u start W. There is no need to wait.

Ater lvl 6:
W -> Q -> E -> R (3x) (enemy is stunned) then release Locus of Power flash next to the Enemy and then Q again.

In your early game your Mana is very limited. So dont waste it to Minions. Try to get some last hits and spend some Q spells at the Enemy.
Dont try to go in 1 vs 1 fights. You will probably lose.

When you are laning use the high grass to hide and poke the enemy with W -> Q.

If a meele-Champion trys to engange you: E -> Q (he is stunned) and then fall back.

Try to keep one of your enemys at about 50 % health. After you reach lvl 6 you just need to do your full combo to get a kill.

Be sure to have enough Mana when you start the first ulti. When u are low in Mana u better wait 1 more Minute to be sure to complete your Combo.

If an enemy is low at health and is trying to teleport back next to his tower use your
W-Spell and then Q Spell to get the kill.
Because of the huge Range, you can stay out of the turret range, and most of the Players wount expect the Range and the Damange of your Q Spell.

Dont try to go in 1 on 1 fights when your E Spell is on cooldown.

When you see that you get enganged by a Champion you have to do your E and Q Combo. Dont hit him with Autohit anymore, just run and wait for E-Spell cooldown. If the enemy is silly enough to follow you, E and Q him again and flee. When he reaches about 40% health and he is still following you: E - Q - R. When he is still alive : W - Q.

When 2 or more Champions are engaging you try to do a W - Q - W combo. When you get out of Locus of Power (W Spell) you get a few seconds some speed bonus. Use your flash and run! If one of the enemy is using his Ghost-Spell, stunm him with a E Q Combo.

In Team battles your Quest is to stun the enemy DPS with your E then Q Spell. But dont waste your W in the beginning of a fight.
When the first Enemys get low and start falling back, its time to start the Artillery.

W then R and bam bam bam.

Use Q as much as possible. With cooldown reduction runes and items you can cast Q almost every 3 seconds.