This guide outlines how I play Orianna. It allows you to nuke a squishy like Sivir from full health to 0 with one combo. It will allow you to disengage from most gank attempts while both surviving and doing significant damage to the following player(s). It will allow you to chase, and to drop towers. You will be squishy, but far sturdier than any other AP character that attempts to use this item build.

Orianna scales extremely well in all respects with ability power.

Her auto-attack does a portion of her ability power in magic damage, meaning her autoattack will be doing 300+ hybrid damage per shot end-game. Her shield scales with ability power, meaning she will be doubling her effective life by self-casting protect end-game.

Naturally, her ability damage output will scale. Using this build she can nuke an entire creep wave just by casting command: attack.

Her item choice is very restrictive, so with these runes we make up for some of the shortcomings: team-fight survivability and Ability speed. The quints allow you to chase down enemies, or run away that crucial bit faster.

It looks dumb. Before you knock it, try it. You get a ridiculous amount of mana, regen and - most of all - ap. Whilst the +mana snowball effect is unique, the 3% max mana to AP is not. This means that you'll be gaining 12% of your max mana as AP at the end game. This translates to well over 1000AP when you have your last staff.

Mercury treads, because we need as many slots as possible for archangels, you already have speed quints, dissonance and shockwave, and having tenacity beats having spell penetration, unless they really start sucking/stacking magic resist in late-game.

Clarity will ensure you don't run out of mana.
Flash will give you the extra jump you need to either get a gank or gtfo.

Subbing in teleport for clarity will leave you a little starved for mana early game, but provide more mobility for split-pushing lanes late-game.

<rant>
People don't do this enough.

This doesn't mean autoattacking and hoping you time it right so you get the last hit, it means timing your attacks so you get the very last possible hit on the creep, shaving off the tiniest part of it's health, and minimising the impact you have on the creep battle.

Orianna has great escape abilities, but if you've pushed all the way up to their tower when you don't have team support or know that the enemy team are dead/elsewhere, chances are that:
a) You're not getting the CS you should be, because you're afraid to invoke the wrath of the tower/get harrassed and;
b) You're about to get ganked by the jungler/mid. Those gaps in the treeline and the entrances to the river are sources of potential death.

If you and your opponents last-hit, you will be sitting relatively peachy in mid, occasionally fluctuating back and forth due to splash from harass. If your opponents are scrubs, you can last-hit as you are pushed back then start doling out a bit more damage to keep the creep encounters just outside your tower range.

And if you are a complete scrub, this means that you have zero distance to run back into the safety of the tower.
</rant>

Smart cast attack: Shift+Q

Self-cast protect: Alt+E
Smart-cast protect: Shift+E

If you didn't know, now you do.

Use command:attack to scout bushes.

Between clarity and meki's pendant, you should be able to sustain enough mana to keep constant harass on your opponents with command:attack and command:dissonance. With the range of the ball and the damage from that combo, you'll be keeping them under the thumb until you go back to buy, provided you don't take any dumb risks at the start.

Try to avoid command:protect until you get tears, otherwise you'll go oom.

Grabbing tears first lets you start getting your mana bonus up early. At this point you'll want to start using command:protect more. Between last-hitting, flash, dissonance and protect you should be able to survive the laning phase without getting ganked, so boots aren't too much of a priority until you want to start finishing people off.

The obvious combo here is attack/shockwave/dissonance/self-cast protect

Dropping protect on your tank just before initiation is great, as it both gives him armour/shield/magic resist and puts the ball in range of the enemies well before you're in range to cast command:attack. As an initiation trick, doing this then casting shockwave/dissonance clumps, damages and slows opponents for concentrated AoE nuking.

If you're getting spanked by physical damage, sub out a staff in favour of a frozen heart.

If you're getting spanked by magic damage, sub out a staff in favour of a banshee's veil.

If someone tries to gank you:

1) Right click towards a safe place
2) Self-cast protect
3) Dissonance to run faster and slow the chasing player
3.1) Flash?
4) Throw the ball back towards the chasing player
4.1) Shockwave just as they pass the ball

You'll be shielded, out-running them, and stinging hard with all that AP with Flash and Shockwave available in the more hairy situations.

After this happens a few times, people will generally just stop bothering to chase you, unless there are quite a few people there to chain slow. If this happens: why weren't you under your tower, or with your team for the teamfight?

Thanks for reading. I hope this is of benefit to you. Please leave me some feedback if you feel so inclined!