Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
I'm still working on the guide over time, but this a comprehensive view of what my Soraka looks likes for ranked play.
Okay let me explain my runes:
For Marks I go with Magic Penetration so my Starcalls and Infuses do just a little extra damage, and also do true damage to creeps/minions.
For Seals, I chose specifically for my Soraka runepage, Flat Mana Regen. I need the extra mana regen at level one to keep the Starcall spam up so we can ensure a kill, if Soraka draws first blood, it usually crushes the enemy teams morale.
For Glyphs, I go with Cooldown Reduction Per Level, With Death Fire Grasp I have just under max cooldown reduction at level 18.
For Quintessences, I choose Flat Ability Power, Because the 15 extra Ability Power at level one gives me 30 AP with Doran's Ring, so I don't need an AP item so quick, and it allows my level one heal to be not quite so ****ing terrible.
I run with 9/0/21 Masteries.
1/3 Deadliness, Since I don't use exhaust or smite, this is the best use of the mastery point, Soraka does have a 2% base crit chance so whatever.
3/3 Archmage's Savvy, Pretty self explanatory, AP per level, whats not to love.
4/4 Sorcery, CDR, Gotta spam dem Starcalls, heals, infuses...
1/1 Archaic Knowledge, you don't get a whole lot of magic penetration as Soraka, so this helps out with anyone who has MR before you've Starcalled them 8 times.