First of all,sorry for my english xD.
Orianna is a very versatile champion, she can play as ap or support but she is quite difficult to use, even so, is very fun to use ^^

The skill sequence is: Q+W to damage the enemy, when they are damaged use Q+W+R you can also use E on an ally and use your ultimate from him.

Orianna needs runes of magic regeneration, but its not really necessary on midgame-lategame, so you can chage it and take ap runes.
the quintessences of movement speed are also a good option if you have enought ap.

Pros:
lot of versatility
very fun to use
great damage and support
lot of range

Cons:
waste lot of mana
difficult to use

I'll try to finish it al fast i can ^^