Flash is flash. Escapes or for Zhionya's Ults. Standard Summoners spell on most champions.

Exhaust to Slow the opponent's movement and attack speed. Great for offensive or defensive play

Heal and Ignite also very useful. However I try not to get kills so I stay away from Ignite and I normally like Heal on my ADC.

Pros: If played well she is one of the best Supports in the current meta (4.13). Her Q/R are huge for fights and Sheild can save teamates.She also counters some of the other strongest supports including Thresh and Leona. Also very strong vs Blitzcrank and good against Braum.Very strong early game. Great at stopping ganks.

Cons: Not the tankiest. She doesn't really fall off late game but she doesn't scale as well as someone like Thresh or Braum. Her main initiation is Skillshot. Positioning very important to land Q's and good Ults. Quick reactions needed for ultimate effectiveness on Shields.

These are the masteries that I like to use, although there are many different options. This layout allows for maximum gold income w/o farming and gives extra health, CD and mobility which is very good on supports.