For the time being i will focus on Anivia Support:

What makes Anivia a good Support:
-Good CC
-Good DPS
-Strong earlygame
-Unique and creative
-Flex/Bait Pick
-Very Hard to gank
-Good scaling
-Game changing Abillities (W)
-Good Gold usage (DPS when Ahead)
-Decent playmaking when Behind (Passive and W)
-One of the best Item Usages (Zhonias, Bandlepipes, Liandries, Malignance, Solstice Sleigh)
-Blindpickable
-Being able to manipulate waves with your W (Freeze or Push)

What does Anivia lack:
-Enchanting
-Mobility
-Tankiness

Playstyle

Depending on your ADC you want to play arround their Strenghts:

- Closerange high output ADC -

It's pretty simple you want to catch your enemy offguard with your W and enable your ADC's to force a fight with no escape for them.

- Long Range medium Output -

You want to play more poke oriented with shorter trades, it's also viable to safe your W for safety.

Tipps:

You should learn tricks about your W
-> Canceling Jumps
-> Wallwalking
-> Movement Manipulation
-> Stun when parralel
-> Cancel Abillities (Nunu W, Sion Q/R)
-> Cancel Hooks (Blitz, Nautilus, Thresh, Pyke)