- Riot Kades -
I reference Kades because he has more experience playing Mid Soraka then I.
A sizable point to make - Mid Soraka is going to have a great KDA ratio, but a horrible K to Deaths ratio.
-Runes/Masteries for a focus of that extra near 20% CDR, FREEING up an item slot.
* I've played an AP Bruiser version of Soraka since beta- back when there was no que dodge penalty and I'd be trolled just for picking her. I don't know- I think at the time there was something very appealing about mastering the perceived 'worst' champion. Then I just clicked with her, and while I can play other champions/roles decently, taking Soraka mid or top is definitely what I'm best at (depending on the current meta).
*I don't have an exact number, but I would imagine I probably have around 2-3k Soraka games played if you include both seasons, normals, and preseason/beta. It's kind of absurd, honestly.
With all that said, here's where I'm currently at with Soraka in Season 3: CDR
Easily, the most important stat to get is Cooldown Reduction.
*You max out at 40% CDR, and nothing helps your DPS or utility more than maxing that out ASAP. Soraka's ratios aren't actually all that great- she only gets .4 AP on Starcall, .45 ratio on Ancestral Blessing (heal), .6 ratio on Infuse, and .7 on Wish (ult). So rushing or statting for AP early game I've personally found to be fairly ineffective. However, due to having a naturally low cooldown on Starcall (2.5 seconds) and the spammable nature of the spell (combined with the added utility of the additional MR shred), maxing cooldown first is extremely effective.
*Right now- and I change this often- I'm gaining 10% CDR from my masteries by going 4/0/26. I get an additional 10% CDR from runes by level 18 so that I can max my CDR by just grabbing one item. A lot of stuff changes for me as I continue to discover new things about Soraka, but maxing CDR has been a constant for a few years now. It is extremely important.
*Due to my playstyle, I grab Heal and Flash. The third heal I've found to be clutch in teamfights, but I could make an argument for Barrier or (surprisingly) Clarity. Both are very effective, though Clarity is often ridiculed- that rage tends to roll off of me, but you should expect it if you give it a try at higher (or mid) elos.
Dependence on Visibility
*When I head mid, I tend to depend on visibility to avoid ganks. I typically grab two wards when I head back so that I can ward both brush on either side of mid. People see Soraka mid, and they love to gank her.
*Contrary to popular sentiment, I've found Soraka to have a relatively weak laning phase while she really comes into her own during mid-game teamfights. She pairs best with a healing support on her team (Sona, Alistar, Taric are ideal) and then you have near indefinite sustain mid/late game. You can feed your healer mana to spam her heals and you have your larger burst healing to help out.
*So I play fairly passive during the laning phase. I often tell my jungler to focus on the other lanes, and I play passive while I build up my first few core items.
*Due to mana cost changes from her most recent nerf, you really have to get a large mana or mana regen item. I've been rushing Athenes to give me both the CDR and mana regen, but I could make an argument for going Tear/Frozen Heart or possibly Catalyst/FH/RoA. Find what works for you; just max that CDR early.
Max Q, Watch Ability Icon To Bush-Check
*For Skills, I max Starcall first. I use it at level 1 in order to scout bushes as I'm walking in (if you spam q as you walk up to a bud, when it goes off, you know there are people there ready for a gank). I get infuse at 2-4 depending on how much damage I've taken (typically 2) so that I can walk up, silence the player, and hit them with a starcall and walk back. It's effective, but you can't do it too much or you'll inadvertently push your lane into a bad position. I typically max heal second and infuse last, getting my ultimate at 6, 11, and 16.
*After Athene's, I've been building Rylia's to Liandry's- you get an insane amount of damage at this point. After that, I can get a Deathcap or more but into more survivaibility based on their team. A deathcap really helps your heals and helps your Starcalls quite a bit.
High Sustained DPS instead of Burst
*The last point I'd like to make is about the damage that Soraka can do. It's commonly thought that she does terrible damage in teamfights- this is completely inaccurate. She does insane damage in teamfights- it's just that almost none of it is burst. But even with 0 ap, you're doing 160 damage (pre-MR) to 5 people every 1.6 seconds. That's 800 damage every 1.6 seconds to their team. It's not burst, but it is substantial. Also, you have the ability to heal your team (3 times with AB, Wish, and Heal SS) and shred their MR so that other AP Casters on your team do even more damage.
*Even when I check "damage done to champions" I'm often the highest damage dealer in the game. My KDA might suck (I've never cared about kills, I care about wins) because I'm not necessarily doing the finishing blows, but my teams win because I do so much AOE damage plus utility.
Mid Soraka isn't for everyone, but if you have any other questions, I'll be happy to help out how I can.
TLDR, Max R, Q, W, E with one point in E at 2. Get 20% CDR with Runes and Items. Get max CDR with one item (I rush Athenes). Then grab Rylia's -> Liandry's.