I have played Orianna as main on season 5 and early season 6 with couple hundred games on Gold/Plat. Orianna is very stable champion and can deal against any champion someway, so its pretty hard to totally counter her. I keep updating this guide as I see its best to play Ori. So updates are ongoing.

Seems that Frost Queen Claim can work for Ori too, better against some setups like talon/other stealth. But in general Ori works best when she is doing loads of damage (early and during whole game, so without Frost Queen's Claim) and is more fun to play that way.

Orianna works best if you have team composition which is has easy to follow champs like Dr Mundo/Amumu but sure there are also good combo options with champs like Malphite.

Orianna seems to be more popular on later plat/dia/master. Reason might be that players do not do so much plays that their team do not expect. So the team is easier to follow.

+ Pretty safe pick.
+ Ultimate can be game changing.
+ Can help the team even with low farm, thou damage will be very bad.
+ Farming is quite easy.
+ Can use all abilities over a wall and 'scout' with ball.

- Mana is problem.
- You have to get some kind of mana item early.
- Learning to control the ball well takes a lot of time.
- Not very good avoiding ganks.
- Ultimate easy to mess up.

Early game for Orianna like most other champs is focused heavily on farming. But mostly you need to farm with your AA's so you will have some mana for poking. You can try to poke through minions with Q. but beware that Q will then lose some of its damage. Unless you are max mana, you should avoid using W,E when poking since they they do not have as good mana/damage ratio than Q.

Orianna is not very good avoiding ganks even with +movement speed and extra vision from Q. So use wards and do not push unless you are sure you can get away.