: Exhaust is any supports best friend. Slow them down so your ADC can get a kill. Try to use it on champs the are low heath and are getting away.
: Flash is just nice to have in most situation. You will most likely use it when you are trying to get out of a team fight that your team just lost.

Soraka use mana up quickly if your ADC is taking a lot of damage. Try not to spam your ability's but I included some item like Chalice of Harmonyto try and keep you mana up. The rest of the items are either for health or for your ability's to be stronger.

DON'T spam your W. It takes quite a bit of mana and using it every time it's up will make you go back for mana and you want to be in lane as much as possible with your ADC. Your E also uses no mana so you can spam that on enemy champs only if your ADC isn't out of mana. Don't be hesitant in using your R key . it have an average cool down but it heals ALL ailed champs so use it to save your buddy's. your R and W are nice in team fight to heal someone who is almost dead your job is to keep your team alive for as long as possible.

I call them the Jewish mastery's. They are there to get you as much money as possible since you shouldn't be last hitting minions. There are also some offensive points so you can do something with your ability's.

Soraka is weak early game. These runes will help you if the enemy ADC hits you. There are also some money ones in there to help you even further in your quest to be the riches person in game.