Once you get into lane just farm up and try not to miss CS. Especially for siege minions, if you're unsure of whether or not you can get it, use your Q. If your opponent is going for a CS and you are fairly sure you can land a Q sweetspot on them (the middle of the Q) then go for it. Your Starcall has absolutely insane base damage and will do a lot of work. Once you get around 750-800 gold, go back and buy your Tear of the Goddess. If your opponent looks like they're gonna push really hard and try to chip a lot off of your tower, then throw out a ton of Starcalls to push back. Buy a tear and a couple of health pots.

The most important part of laning phase is to farm up. If you reach your core build that has capped CDR you will provide an unimaginable amount of assistance to your team.

By now you should have your ult, Wish. Watch the health of your teammates and make sure you ult to save them. Easy way to do this is just check their portraits above the minimap. Even if it isn't needed it's better to be safe and use it anyways, unless you know that as soon as your ult is on CD you can die to your lane opponent.

Now that you have your core build of lucidity, tear, and athene's, you can spam your skills to death and almost never run out of mana. Start using your Q to farm more safely since you probably won't be able to do direct trades with your lane opponent. All you have to do is farm and you will carry your team in teamfights. Just like early laning, throw Q out to harass because it will do a LOT of damage. Save your Equinox unless you know you won't need it for the next 15-20 seconds and you can benefit from the basically unavoidable free damage it gives. If your side laners are doing fairly well, push your wave up really hard and go roam. When you roam you will have 2 main options. The first is that you can simply force the enemy laner out with your very strong and safe poke then proceed to take the tower, or you can just tell your laner to dive and get a kill because of the amount of heals you provide for them. With Equinox it also makes it hard for the enemy to flash when being dived, or to even fight back at all.

This is when Soraka mid becomes a monster. With your Luden's finally complete and maybe a liandry's/rylai's, you deal a good amount of damage with the insane poke you have. Your tear should also be fully charged and hopefully built into a Seraph's Embrace by now. Feel free to mash Q and throw out Starcall whenever you want. It will tell you where champions are because of the healing effect that appears if you hit an enemy.

At this point you're ridiculously mobile and you're pretty much as hard to kill as a Janna. With all that movespeed, the slow/silence on your Starcall and Equinox, the missing health-scaling heal on your Starcall champion hit, and a bunch of other tools you have, the enemy team seriously has to focus you or be punished for it. Your Astral Infusion will be up every 1.2 seconds and heal for 400+ HP.

Just throw your Astral Infusion on whoever is low but never, ever make yourself too low to safely participate in the fight. During the fight, wait for the right moment to use Equinox to disrupt an enemy's combo that could potentially kill a team member. If you get a good engage, from, for example, a Malphite ult, then throw it down so that your opponents have no options aside from attempting to leave the field. Remember that your Equinox damage is basically instant so Flash + Equinox is a guaranteed kill in most cases.

If you are getting focused it is pretty easy to deal with it. Just use your Seraph's Embrace active, silence whoever is on you, then pelt them with Starcall as you heal back lots of health and watch your team wail on them. If you aren't getting focused, freely throw your Q out because you actually have more DPS than most AP mids in teamfights; you just lack burst damage. Heal up whoever is low, and if you need to save someone use Wish Just remember that Wish heals for a lot more on allies below 40% health.

Even if you lose the teamfight, if the opponents are really low keep on spamming your spells. You can kite the hell out of anyone you want and you can basically force any opponent who is low from doing ANYTHING. You are still very effective even if you are the last one left alive on your team. Try and bait your enemies to chase you because they will rarely ever be able to kill you and you can waste their time while your own team revives.

Liandry's Torment is an item I normally go on Soraka. Since you are building mostly CDR and not much AP, coupled with the fact that Soraka doesn't have impressive AP ratios but really good base damage, magic penetration is a very very strong stat on her. I find this item to provide the perfect spread of stats for almost any situation: A bit of health, a bit of AP for your spells, a good amount of flat mPen, and a tank shredding passive so that your DPS in fights affects even the enemy tanks.

Rylai's Crystal Scepter is another really good item. If anything, it's great for peeling for your team or catching people out. It is more of a defensive option for your team rather than the offensive one with Liandry's provides. It also makes it really, really easy to catch enemies in your Equinox snare.

Dead Man's Plate Is a strong defensive option. Since you don't use your AA in teamfights you will consistently have the extra movespeed which makes you even harder to catch. However, if you position right you most likely won't have the problem of dying in the first place.

Warmog's Armor. People chase you after a teamfight and you're low. You kite them with several Starcalls and other spells and heal all their damage back. When they finally burn their flash to get to you, they now realize that all this time the passive from Warmog's has been healing you back to full health. It's pretty funny. Also a really great item for more heals on your teammates in general.

Soraka Mid doesn't have the best laning phase but can still be very safe in it; just farm up so that you can get your items and then you're a monster lategame! You can easily carry teams without even realizing it! You have amazing sustained DPS, amazing sustained healing, and an instant AoE silence which is one of the most broken CC effects in the game. You are also impossible to catch and huge baiting material for your team. Even if it seems like a joke, try it out sometime because Soraka mid is deceptively strong.