Xerath is usually played in the mid lane as an Ap carry but he's also a fantastic support. He's a very unique champion on the rift as Xerath's range dominates the lane, all of his moves are fantastic poke and therefore he can dominate the lane phase against other Ap carries like LeBlanc, Annie and Ryze.

Ap carries are usually the main target in team fights, their burst throughout the game is incomparable which means a fed Ap carry on the enemy team is a disaster. Xerath is a huge counter in the lane phase as his poke is huge, his Q,W and R can't be blocked by minions are are long range and abusing his passive for the mana regen Xerath can keep the opposition out of lane stopping them from farming. If they're not in lane, they're not getting farm or experience.

Ap quints and glyphs are a must, you need the Ap especially early game to shut your opponent down and keep them out of lane. Ap carries fall far behind when they don't have gold and are under leveled, if you finish the lane phase with more gold, a higher level and more kills you've shut their carry down ruining their team fighting chances.

I like the magic pen marks, since Ap carries fall behind against tankier champions they help close the gap to even out the chances, with a void staff, Liandry's and sorcerers boots their magic resist is lost.

Seals are the defensive runes, take what you like here as you shouldn't be to close to need them, armor or health runes should be taken as Ad mids ruin Xerath's plays.

Grab all the Ap masteries you can, then you can make a choice between 9 points in defence or utility. Since Xerath's passive is amazing for mana sustain you don't particularly need the mana regen from utility.

Xerath doesn't have an escape especially from ganks, your E and W can help you but they're not a hard escape. I take flash and barrier/heal, all give you a second chance to escape and barrier and heal take a huge chunk out of their ignite if they use it to finish you. I don't take ignite on Xerath due to the fact that you shouldn't be that close to them anyway.

Doran's ring and 2 health potions is a great starting set, they will help you to stay in lane for a long time before your first back.

All depends on who you're laning against, your gold and how the game is progressing. If I'm against an Ad champ like Zed or Kha'zix I'll rush a Zonya's hourglass since most of them have a gap close to jump onto you.

You can chose between full Ap or a tanky Ap version. Deathfire Grasp is there for Ap, you shouldn't really be close enough to your target to even use the on use and by the time you've used all your spells including your ultimate the DFG would have expired. I usually build tankier when they have a few assassins or Ad, it doesn't matter how much Ap you have if you're dead before you can land a burst!

Xerath's passive is amazing especially during the lane phase, it allows you to constantly poke whilst being at a safe distance. The opposition won't engage as they should be to low to be able to do it safely, poking them to 10-20% till they have to back is successful, even if you don't get the kill they are still out of lane losing gold and experience!

I take the shocking orb first, simply to help with a leash, CC to engage on the invade or to stun whilst running from their invade.

Q is a great poke, wave clear and with a small CD its perfect! W Second, nice poke over the minion wave with a good range, slows if they are hit in the centre which is hard to land but if placed behind them they usually panic and walk into it anyway!

Max E last, the stun duration stays the same through the levels and even though its a great part of your kit it can easily be dodged and impossible to land if they are behind minions.

Take your ult whenever you can, be smart when using it as the cd is long.

Abuse your passive and poke, you should never be on full mana. Xerath can be hard to last hit with so try to use your moves to get CS and poke at the same time, if they're smart and can dodge the skill shots then try to wait for them to engage on you before bursting. Engage with your E, The longer the distance the better the stun as the distance elongates the stun up to 2 seconds. Once they're stunned land your W on the centre of them for the extra damage and then Q, Simple :)

If your going to get a archangel staff you may want to grab the first few blues, these will help you clear the waves very quickly and keep your lane pushed whilst poking your opponent. Try to roam when you can, your range and CC is a nice gank, as your teammates to call out if anyone is low, if a ward catches someone low be smart about it. Blowing your ult charges can be easy, if they are low and near the bush they're most likely recalling, if you were in that position would you back in that bush, if yes they why not fire one there. I've had a lot of kills when my lane opponent goes for his/her blue and I fire it into the small bush adjacent to the blue as their recalling.

Stick at the back in teamfights, most of your moves are aoe so try to hit more than one person especially with your Q, if you're fed you're a major target so if they're coming for you use the W to slow and E to stun, then just kite whilst your team cleans up. Rylai's works well when kiting and makes landing your skill shots a whole lot easier.