Soraka Mid Laning
I used to play Soraka as a supporter, but then I totally stopped doing that, since she was nerfed hard. Huge CD's on her abilities make her almost useless unless the team fight draws on. Since you don't get any gold you can't even compensate for it.
Wait...Gold...Farm...Mid-Lane! Yes, that was all I thought. Mid Laning with Soraka is fun, delicate, effective, but almost always you get yelled at by team mates :P
Farming will be your number one goal: The more farm you have, the more gold you have and that translates directly into your healing power by mid-late game. You should NOT expect to many kills with this build, even a AP-Soraka is suportive. Without further ado, I present to you Soraka Mid Laning.
Level 1-Level 4
Pick up your Meki Pendent and 2 Health Potions. Head of to mid lane, cover your jungler if needed, help with a jungle invasion. No matter what happens you have to skill Q Starcall first.
Let's skipp to when the minions arrive: Just walk into the gap between caster and melee minions and spam Q. Try last hitting the melee ones, the casters should automatically die to your hands. If that Annie thinks she can harass you just keep spamming Starcall, pop a Health Potion and throw a couple of Autoattacks her way.
The first wave of minions should be dead by now. Since you pushed so hard you should reach level 2, with your opponent still at level 1. Throw an Infuse at them if you mana looks fine, otherwise Infuse yourself. Go back a couple of steps, you don't want Big Bad Warwick to gank you.
When the next wave of minions arrives follow them and continue to happily spam Starcall use Infuse once it's of Cooldown and laugh at Annie when she fails to last hit the minions under the tower where you pushed them.
After continuing this for 2 minutes or so you reach lvel 4 this means your damage has increased by about 40%. Go towards the enemy now and stop pushing as much. Take last hits, Infuse the enemy, or Starcall when they get in range. When they harass use Astral Blessing, right now your goal is to keep them zoned for as much as possible.
WARNING: Most Junglers will start ganking just about now or maybe a little bit earlier, so with you standing that far over extended by the enemies tower you might want to ask the supporter to use Clairvoyance into the brushes at the side of Mid-Lane.
However as soon as you can afford Tear of the Goddess I suggest you go back and buy it, so you can get those 1000 bonus mana as quickly as possible. And yes you do that by...spamming Starcall some more!
After you got Tear of the Goddess (level 6)
I don't have a clue what level that might be, but as soon as you have it you want to spam your spells in 3 seconds intervalls, so you get the stacks as quickly as possible. ( It is possible to get the full 1000 mana in around 12.5 minutes)
Since you now have bassicaly unlimited mana you will want to harass as much as possible, healing back any counter harass. Should you be able to force the enemy back, then push the minions to the tower and depending on how much health you have left, either go back yourself, or gank a side lane, preferably a duo lane, since Starcall is AoE.
When ganking, first go into the brush, then depending if the enemy is so overxtended that you can easily get behind them, activate ghost, or if they aren't that overextended, wait to use ghost untill you enter the lane. Then right before your first Starcall, activate Surge and QQQQQQQQ away. Heal at need and obviously Infuse the target with most dangerous spells.
POWERTIME! The enemy team doesn't have enough power to nuke through your heals just yet, and you deal terrific damage. Roll faces with Ghost, Surge, Starcall combo.
Your power time is over, try to stay a little bit more in the back of the team, concentrate on healing and Infuseing, Starcall's range is so tiny that getting close enough to use it puts you into to much danger. If you didn't get your team ahead before now, you failed. (Sorry, but that's the way it is)
You can push exceptionally well, nuke waves 2-4 times and all are dead and also backdooring is easy since you can heal the tank, making him much more durable.
First of all... You do NOT want teamfights. If your team comes to push mid, tell them to get lost. The best senario for you are 2v3, 3v3 or 3v2 skirmishes, that being said, I see AP- Soraka as a possible Dominion character.
Anyways, in teamfights is to much damage, you want the damage output to be low enough for you to heal back large parts of it. Your number 1 healing target is YOU. Because when you are dead you can't ulti anymore, and what is more, can't chase the enemies. You are a awesome chaser, since you have an AoE slow once you got Rylai's Crystal Scepter.