Hello this is verxx and I'm here to bring you the best way of playing Orianna. She's an extremely fun character to play with some of the most interesting mechanics in League of Legends.

Warning: Orianna, like any other champion, should be built according to what is going on in the game. I wouldn't use the item build at the top as is. Please read the Core Items and Viable Items sections below to learn what some of the items do and when to get them.

Why build AP?
"Why verxx are you building AP? Orianna is support! It even says so on her character sheet! WHHYY???" Because Orianna is one of the best AP carries in the game. She deals massive damage early/mid game, amazing laner, has good escape and her ultimate is one of the best team fighting abilities in the game. In my opinion Orianna should never be built as Support (even though thats what the riot tag says). There are many characters that fill the support role MUCH better ( Janna, Taric, Sona, Soraka) and it will be a waste/detriment to your team to build her that way. I also dislike the AS approach because she is far too squishy to be auto attacking with. AP carry is also the way that Orianna is always built in 2000+ ELO matches. Please read and try the build before judging.

Pros:
- Massive damage early/mid game
- Good damage late game
- Command: Shockwave extremely good for ganking and teamfights
- Good escape with Command: Dissonance + Command: Protect
- Amazing laning and zoning
- Awesome farming
- Good shield in late game.
- Fun mechanics!
- Crazy range

Cons:
- Squishy
- Mana dependent early/mid game
- Reliance on getting blue
- Needs solo lane (preferably mid)

Greater Quintessence of Ability Power and Greater Glyph of Scaling Ability Power for extra Ability Power to increase your damage.
Greater Seal of Scaling Mana Regeneration to help with early mana problems.
Greater Mark of Magic Penetration magic penetration for even more damage!

You could also use some armor/magic resist runes for early survivability but that is not advised since mana regen helps you much more in your initial laning stages.

Masteries are standard caster masteries (9/0/21).

Take mid or top lane! Orianna needs her farm and her level advantage as an AP carry so she should be in a solo lane. She is also one of the best laners in the game and can easily zone out most opponents in mid due to her extreme range. She is a very good counter to most of the AP carries that you will see in mid (ie. Annie) but she does have a weakness for gap closers like Katarina and Irelia. They can easily warp to you without worrying about the ball catching them while they try to get in range.

I take one point Command: Protect first, as it offers you some base armor and magic resist and a shield for those emergency situations. Concentrate on last hits for the first 3 levels. Start with Regrowth Pendant as this allows you to stay in lane and take harass until you can start zoning your opponent out of the lane at level 4.

Once you get 2 points in Command: Attack the fun begins. Use Command: Attack constantly to harass your opponent while continuing to last hit. Positioning and hitting your opponent with this skill is essential to laning as Orianna. You want to always make last hitting a priority though. Farming is very important as Orianna.

You want to add one or two points into Command: Dissonance. But do not use this skill to harass. Command: Dissonance is extremely mana hungry. Command: Attack has the best Mana to Damage ratio so you need to harass with it to get the best use out of your lackluster mana pool. If you get into a sticky situation and need to retreat, simply press ALT+E (this will use Command: Protect to shield you with the ball) and W ( Command: Dissonance). This combo will give you shield and protection from incoming attacks as well as a speed, slow and damage aura to help you get away from any ganks or attempts to kill you.

Once you hit level 6 you should have either made your lane opponent go back to base or you have left him with a sliver of life. If your opponent stays around with low health it can result in a very easy early kill for you. Orianna's burst is Command: Attack + Command: Shockwave + Command: Dissonance + an optional Command: Protect. You can use this to finish off your opponent and give yourself an early kill.

On your first trip back you should get Philosopher's Stone for mana regen and some extra survivability. Also you want to get Doran's Ring x2 for more mana regen and ability power to harass your opponent like a boss (Doran's items are always great early game and very cost effective). Boots for mobility is also a good item for your early game. Continue farming and harrassing your opponent.

You want to get blue buff around level 10-11. Orianna needs blue buff. Ask your jungler to give it to you or get it yourself. Orianna is the most beneficial recipient of blue in your team and it will allow her to harass mid lane, farm like crazy and pull of some awesome ganks in side lanes. From now on you need to be getting blue buff as soon as it is up.

Continue to farm the mid lane once you get blue buff. Spam your abilities like crazy, even Command: Dissonance. She will be impossible to do anything against since you will have the ball changing position every 3 seconds and Command: Dissonance going off every other Command: Attack. You will push your lane opponent to his tower.

Be sure to always be using Command: Attack to check bushes everywhere you go, this is one of the best utilities Orianna has.

If you have Command: Shockwave up and your opponent has low hp then you should try to kill him, otherwise push your lane up so that your opponent loses xp and last hits and go to another lane to gank.

You can gank other lanes with your burst ( Command: Attack + Command: Shockwave + Command: Dissonance + an optional Command: Protect) since it does SOOO much damage and allows your teammates to also catch them while they are slowed or knocked up.

Once you are done ganking you can return to your lane and continue farming. Always try to be farming or ganking. One neat tip is you can jungle very well with orianna. From middle lane you can throw your ball with Command: Attack into the enemy wraiths and use Command: Dissonance to kill them.

Your goal for next trips back is Needlessly Large Rod if you can get it, otherwise get Blasting Wand. Eventually you want to make the Rabadon's Deathcap. Also be sure to be getting wards. Everybody needs to get wards

Farm whenever you can - you can destroy a whole wave of minions with 3 abilities. Command: Attack into the middle of the caster minions, Command: Dissonance and Command: Protect on yourself to send the ball back thru melee minions. You can farm your own and enemies jungle as well. You do moderate damage to towers so you can try to push towers.

Poke your ball everywhere especially bushes. This is a very good scouting technique that has saved my team from many messed up situations.

In a team fight you constantly want to move the ball with Command: Attack to do damage. Also doing this will help you find a good opportunity to use Command: Shockwave. Ideally you want to hit the middle of the enemy group with Command: Attack then use Command: Shockwave. This should bring them all into one point in the middle of your ball where Command: Dissonance + Command: Protect will do massive damage. This combo works especially well on enemy carries. There have been times where I have even taken out 3 of the enemies carries before in one burst combo in the middle of the teamfight. With Orianna's range this is even possible when they are standing behind their tank. Another usefull effect of Command: Shockwave is stopping channeling spells. If someone like Katarina is ulting in the middle of your team you could try using Command: Shockwave to interupt it, although sometimes it might be more beneficial to hit more people but it is still good to keep in mind.

Dealing damage and using your ultimate correctly is your number one priority in a team fight since you are an AP carry. Although if you see an opportunity where you can save a teammate with Command: Protect you should do it. A good example is when a teammate is retreating with low health. Throw Command: Protect on him and active Command: Dissonance. This will give him a shield and a speed boost allowing him to get away from immediate danger.

There are 3 starting builds that I have found viable for AP Orianna and I will talk about them below.

Philosopher's Stone

This starting build allows for some good lane sustain early/mid game and gives you good mana regeneration after your first trip back. This is good against some opponents that might harass you and give you problems before level 5 when you can start zoning them out of the lane. Also this should be sold later as you are running out of slots.
Regrowth Pendant Health Potion -> Philosopher's Stone

Tear of the Goddess

This gives you even more mana for early game/mid game and allows you to harass like crazy! The downside of this is that you don't have as much lane sustain since this does not help your healing. Tear of the Goddess also allows you to rely a lot less on Blue. Use this for opponents that you know won't give you trouble before level 5-6. Late game you can turn this item into Archangel's Staff for mana/AP.
Sapphire Crystal Health Potionx2 -> Tear of the Goddess

Catalyst the Protector

I've seen this build used decently in 2000+ elo. I'm not a big fan of the catalyst or the items that it builds into for Orianna because she already has pretty decent survivability. You could build this if you anticipate lots of stuns later on in the game and you will be getting a Banshee's Veil.
Sapphire Crystal Health Potionx2 -> Catalyst the Protector

Core Build

After you get your starting item that takes care of your mana problems you should be looking at getting Boots and Doran's Ringx2. This will give you even more mana to harass with as well as some good AP and survivability. Doran's Ring is an awesome and extremely cost effective item for casters and that is why I use it. Sorcerer's Shoes should be gotten right after for more damage.

Next you want to get Rabadon's Deathcap as it provides a LOOOT of AP and will make your burst insane during the mid game. This is also a standard AP carry item.

Here's the tricky part. A lot of these items are situational. I wouldn't follow the item build at the top exactly how it is. You need to learn what these items do and when to use them. They are all viable items but you will need to buy them in the right order depending on how you are doing and the enemy team composition. Questions to ask are: Do they have magic resist? Do they have lots of stuns? Am I getting focused a lot?

Archangel's Staff
Very good item for Orianna that gives lots of AP after getting Rabadon's Deathcap. You can stack multiple of these for more AP lategame as Orianna needs lots of AP due to her high survivability and relatively low AP ratios. This has a non-unique passive that gives 3% of MP as AP bonus. Very easy buy if you got an early tear otherwise you might want to get a defensive/magic penetration item first. Be sure to buy these whenever you don't need anything else (Defence/Magic Penetration).
Note: I believe this item is great to buy for Orianna late game even without an early Tear of the Goddess. It is the highest AP item in the game aside from Rabadon's Deathcap even without the extra mana from the passive. Due to high survivability and semi low 0.6AP ratios on her abilities, Ability Power is the most demanded stat in late game. When you have 2k Mana you get 105AP from the staff. Easily the highest AP item you can get late game.

Morello's Evil Tome
CDR, AP and mana regen are all amazing on Orianna and this allows you to get close to 40% CDR with blue buff. Poke spam everywhere!

Abyssal Mask
Another great item for Orianna. I favor this instead of Banshee's Veil or Void Staff when the team doesn't have too much magic resist and not many stuns. AP, Magic Resist and lowers Magic Resist for other champions. Awesome!

Void Staff
Get this instead of Abyssal Mask when the team has a lot of magic resist. Don't get both.

Banshee's Veil
Get this if you find yourself being focused a lot and stunned/suppressed. This is also good against AP heavy teams This should help your survivability a lot more.

Zhonya's Hourglass
Get this if you find yourself in trouble against AD heavy teams and if your team is letting somebody through like Lee Sin or Irelia to take you out. Make sure to use the active when you are getting jumped.

Mejai's Soulstealer
If you are a fan of stacking items and you are doing good in the game. This is cheap for how much AP it can possibly give you and Orianna has very good survivability and range to make this worthwhile.

Elixir of Brilliance
Good to get after 25-30 minutes for extra AP and CDR.

Sight Ward
Everybody needs to buy wards!

Since Orianna has a very unique mechanic, there are of course some amazing things you can do with your ball.

- Defending your self! Everybody should know about Self Cast. This make you can an ability on yourself. In this case it is Command: Protect. Simply press ALT+E and the ball will form a shield around you instantly. Use this to return the ball to yourself, in emergencies or to block enemy harass.
- Quick Escape: Hold down ALT. Press E ( Command: Protect). Press W ( Command: Dissonance)
- Rescue Teammate: Command: Protect on teammate. Command: Dissonance will speed him up
- Speed up minions: Position ball in front of minions, Command: Dissonance
- Small burst: Command: Attack, Command: Dissonance
- Quick Harass from distance (Low MP usage): Command: Attack, ALT+E ( Command: Protect)
- Quick Harass from distance (High MP usage): Command: Attack, Command: Dissonance, ALT+E ( Command: Protect)
- Standard Burst: Command: Attack(to position), Command: Shockwave, Command: Dissonance, ALT+E ( Command: Protect), Command: Attack
- Scout bushes: Command: Attack
- Mid/Late game farming: Command: Attack caster minions, Command: Dissonance, ALT+E ( Command: Protect)
- Give yourself speed boost when running somewhere: Command: Dissonance (Late game you should spam this all the time)

There are 3 combos that I recommend using for AP Orianna:

Flash Teleport
Flash is of course OP on most champions(escape, finishing somebody off, etc). Teleport allows you to be everywhere and farm and assist like a boss. This is also the most helpful setup for people learning to play Orianna.

Flash Ignite
Standard AP carry combo (Flash is op) and Ignite can be used to finish off opponent. This is very prevalent in high elo Oriannas. I honestly don't like it that much because most of the time you zone people out outside of your ball range (which is well outside of Ignite's range). I usually finish people off with the ulti burst combo. It also doesn't stay as usefull all game like Teleport does.

Flash Ghost
Also viable. Ghost is almost like Teleport in a way since it helps you get places faster(teamfights for example). It's also a good escape and chasing tool. I don't like this as much as Teleport since you kind of have a Ghost built into Orianna with the Dissonance already but extra mobility never hurt I guess.