Hey all and welcome to my first guide.
in my opinion, orianna is a great champ which is really fun to play,and even after the nerf which reduced her range /increased her mana costs etc she's still more than viable.

allright here we go.

Runes
I chose only AP runes because it's simply the best for a caster.u could also add mag pen. runes,but only AP is working pretty well for me,as it gives me an extra of 50 ap at start.

Items

okay,starting of with a doran's you go well. It gives you health+mana reg,which you'll need to harrass,especially since the nerf increased her mana costs.As you have farmed enough,and possibly slained some kills,you should go back to get tear of goddess.(i used to get catalyst but i pretty fast realized the extra mana isn't enough.)Instead of it,you should go get a 2nd Dorans,because it makes you less squishy,and possibly some boots.As you have farmed enough,which is pretty easy as orianna,you should go back to get Arschangels Staff+Giants Belt.Then you get ryalis,rabadon(i guess you know why),and as the game gets past 40 mins you should go get Lich banes,which is just great for your passive.


skill sequence


skill priority is r-q-w-e
in early game her shield takes too much mana which you could need to harrass enemies,so i skill it last.

Summoner spells

I allways take Ignite + Flash.

Flash is nessecary to escape ganks,as for every other champ.
Ignite grants me alot of kills,especially in early game.
You could also get Clarity or Teleport,but as I'm a pretty offensive player i hardly ever take one of these.

Okay,your main goal is it to lasthit as much as possibly.DONT use your q+w to get minions until you've bought a tear of godess,and even then u shouldn't do it too often.As orianna deals tons of damage just doing her q+w you should harrass with it as much as you can.But since orianna wastes a lot of mana,you should make sure only to harrass when they're in position.DON'T throw your ball,until you're sure u can reach him.Also ONLY use her w, once you're sure it really hits,because else it takes just Too much Mana.

Allright ,this is when playing orianna gets really fun.
At this point,you shouldve bought a ArchAngels Staff,boots+2 dorans or more.
As you have tons of Mana,u start throwing your q+w at the magican-minions.It should kill them,but only do this if you're sure you've got enough mana to kill /harrass the enemy champ in mid.
Also,this is where Ganks start.Allways get wards,or just throw your ball into the bushes if you feel like you could get ganked:D.

Orianna is just OP in teamfights.
She's like an amazing DMG dealer,and a supporter in one.
put your e-spell on the tank as he jumps in,as example amumu.
As your ball is sticking to him,your spells (w+r) work for the ranged he's in.So once amumu jumps into a teamfight,u activate your r and right after that w.that deals an amazing amount of dmg,and often grants u a win.

Okay,as this guide was my first,try not to critizise me too much:D
yet,you should still tell me what could be done better.
rate+comment etc..