I think Orianna support is viable, her early poke is insane (100-300 damage every few seconds) and she can stack her support items really quickly with the new buffs.
In just ~13 minutes you'll get your final support item. Her late game utility is also quite powerful, a powerful shield that can really help with towerdives, a good movement speed buff / slow to help hunt down enemies or to help escape and a teamfight changing ult.

Early game
You need to constantly poke. Every time your abilities are off cooldown poke. Although don't use your W too much because it costs a lot of mana instead try to sneak in some AA's which do quite a lot of damage because of your passive (this is why you should take attack speed)

Mid game
Your poke becomes a bit less useful mid game so you'll need to rely more on your utility


Late game
Poke is pretty useless late game so fully focus on utility. Look which teammates dive into the fight to shield and ult them, which teammates are low hp / are getting ulted to shield them. And when the teamfight goes wrong, you'll need to get your teammates out with your movement speed / slow. In general keep your teammates alive.