Not Updated For Current Season
Oh Sona...you entered the League of Legends and enchanted all with your amazing melodies...and made your team everything but killable. This guide will help you to create a Sona that can dish out some damage to help her team (Especially in laning/harrassing) as well as heal for crazy amounts with her Aria of Perseverance. I usually go around 5/2/15 or so with this build, and if you play smart, you can lead your team to victory provided they aren't terribad at LoL. :)
-Mm crazy heals
-Great at saving team mates with her speed boost and healing/defense aura
-I don't care what people say. Sona CAN get kills, and you WILL get some crazy assists, especially with Lichbane
-Her Q skill does decent damage
-Great passive. It really hurts a lot at lvl 18. Make sure to hit an enemy with it
-Support auras for team fights
-Bit squishy of course. She's a support champ. If you're not careful, you will die
-Not crazy burst damage
-If the other team is smart, they'll focus you
-You really do want to be with a team mate at all times not only for them to protect you, but to give them buffs and survivability.
-If you screw up, the other person on your team who wasn't fast enough to choose Sona before you is going to complain, probably in all chat :P
Runes, Masteries, Summoner Spells -
Starting with summoner spells: I like Clarity to give you and your lane mate some spammability with skills, and flash to get you out of hot water. Other acceptable choices are ghost (escape), teleport (get back into action!), exhaust (escape), or even heal or rally for support. Other choices maybe aren't the best, but you can choose what works for you.
Moving onto masteries: You should almost always go 9/0/21 or 0/9/21. Sona really needs those utilities to keep her mana up, give her more run speed, and most importantly, cool down reduction and gold. Sona has a hard time farming for gold, so this really does help her out.
For your runes: For marks, you wanna go magic penetration so what spells you do will hit harder. If you don't like magic pen you can always go with something more defense oriented. For seals, I like MP regen/lvl, which should cover you for the whole game. Flat MP regen, or more defensive seals work as well, I'm using what I have on hand. For gylphs, I use CDR per level, because early game she doesn't necessarily need to spam her skills (And that would leave her manaless anyhow), and late game this will cap you with only masteries, Soul Shroud, and an Elixir of Brilliance (When it will be important to spam)
Hymn of Valor
(Stance) - Passive Aura: Sona plays the Hymn of Valor, granting nearby allied champions bonus attack damage and ability power.
Active: Sona sends out bolts of sound, dealing magic damage to the nearest two enemy champions or monsters.
Know it, use it, love it, abuse it. This is your main harassment spell, and it will serve you well. Once you learn how to aim it, you can put some serious hurt on with it. As a bonus, it gives you an your allies some increased AD/AP, making them able to put more hurt on in a team fight. At it's max level, it gives 20 AD/AP which is good enough for your purposes.
Aria of Perseverance
(Stance) - Passive Aura: Sona plays the Aria of Perseverance, granting nearby allied champions bonus armor and magic resistance.
Active: Sona sends out healing melodies, healing herself and a nearby wounded ally.
The heal at max level is 140 (+0.5 AP), which isn't too bad considering how spammable it is (About 4 seconds with CDR). Tack on the 20 DR/MR at level 5 and you have your bread and butter team fight skill. In team fights you'll be spamming this and Hymn of Valor to keep the defense/offense auras up, and giving your team a major edge.
Song of Celerity
(Stance) - Passive Aura: Sona plays the Song of Celerity, granting nearby allied champions bonus movement speed.
Active: Sona energizes nearby allies with an additional burst of speed.
Her most underrated spell. However, good use of this will save your team, and possibly save a tower, when you're spamming it on your way there. It's not a huge boost in stance, but the 8% from the active will get you where you need to go which is why you max it last.
(Active): Sona plays her ultimate chord, forcing enemy champions to dance, taking magic damage over time.
This song saves you. This song saves your team. This song effectively shuts down ults by Katarina, Miss Fortune, Amumu, Nunu, Warwick, Morgana and Galio. This song will grant your team that ace you need. It has a large cool down so use it shrewdly, and smart(ly?).
Meki Pendant into Tear of the Goddess: You want to start off with enough mana regen to spam your spells, and you really want to make your Tear asap, because Sona stacks it pretty quickly. Stay in lane until you have enough for this and your first pair of boots.
Boots of Swiftness and Mejai's Soulstealer: The kind of boots you want is really up to you. If you're trying to do more damage for some reason, get the sorc shoes. If the enemy has heavy crowd control get mercury treds. For all intensive purposes though, Swiftness or Mobility will help you get where you need to go, or even escape faster when necessary. You'll notice I didn't list Mejai's in the main build item list, because I feel it's conditional. If you die a lot, then it's probably not a good idea to stack it. However, if you're up a couple kills, might as well pick it up for anymore you may get. After you get this item, try not to die...you shouldn't be engaging anyway unless you know survival is guaranteed.
Archangels Staff: Hopefully you've built up your tear quite a bit by now, giving you plenty of AP for bursting and healing. You'll be maxing out your MP passive fairly quickly because of how quickly Sona can change stances. With that in mind, you need to be able to change even faster, thus the next items.
Soul Shroud & Elixirs of Brilliance: You need some cool down reduction, but why be selfish about it? Share the love with your allies. The Mana/CDR aura is a perfect compliment to Sona's songs and will give your allies the ability to spam their skills more. With this and masteries, you're at about 24% CDR. From this point on, get some elixir of brilliance whenever you can to cap out your CDR (With your runes) and give more AP. Don't get golem at this point. It's much better in the hands of your allies, and for 300 gold, this gives Sona so much more.
Abyssal Scepter: This item gives more magic resist, ability power, and an aura to reduce the enemies magic defense. More support auras? Yes I say. Always share the love with Sona. Try to always get things that will benefit your team mates as well as yourself, because they're doing most of the killing. Your damage really is mediocre compared to a real mage champ.
Wards - Always, always, always buy wards if you have spare gold! Put them in the bushes in your lane and down by the river. It's entirely likely you'll be the only person buying wards, but it's not a waste I promise you. Being able to see a gank coming will save your squishy *** so many times! People often over look these, but they are so very vital to not dying. I consider placing wards supporting my team with map awareness. :P
Lichbane: If your team is pubstomping and you won't die if you buy this over a more defense-oriented choice, do it. Reason being...you can spam your songs every second now. Song, then auto attack. And this plus her passive is just devastating. Plus, it adds AP and more mana for your Archangels to work off of, so it's not a bad deal. Add on that magic resistance, and it's a great buy.
Aegis of the Legion is great if you and your team need more defense. If there's a lot of damage on my team already, I'll pick this up after Soul Shroud to give my team even more defense. Will of the Ancients is an option if you have a couple of casters on the team. It'll boost their AP and give them some spell vamp. If you get the WotA you now boost your allies AP by 50. You're like a free blasting wand, but better :P An overlooked item, but awesome for Sona. Consider replacing Lichbane with one of these.
This is a nice item if they have a lot of DPS. It'll also cap your CDR without you needing blue elixers for sure. It gives armor and mana (synergizes with archangels) as well as its awesome passive, so it's a good buy if you're down to the last slot.
Innervating Heart Locket - No. No no no. I see so many Sona builds with this and all I can say is it's a huge waste of gold for what it does. The passive no longer affects allies, making it useless for support. Yeah, it has some CDR but there is a MUCH better item, the Soul Shroud. Let's compare:
As you can see, the shroud far outweighs the locket in many categories. A 15% cool down reduction aura is more useful to your allies then 450 mana is to you and 20 HP/5 sec is to them. Saves them from buying a CDR item and may cap one of them if they have golem.
Shurelya's Firecrest - Again, nice cool down and health, but Soul Shroud does the job much better AND shares it with allies. The passive is cool...but you're paying like 2000-3000 gold for a 2 second movement speed boost for the team? Just get Lichbane for the perm 8% boost and use Celerity in times of crisis. Don't waste on an item that's like 3/4 useless stats for you. Let a tank get it.
Rylai's Crystal Scepter - Maybe a good choice, but I don't see her having enough spells to persistently keep the effect up. You're better off spamming Celerity to help your allies catch up to fleeing enemies. You should be behind them anyway.
Zhonya's Ring - If you'd prefer to place this item in there somewhere, be my guest, but I've found she really doesn't need it. If the game is loooong and you never got Mejai's, maybe put it after the Abyssal Scepter.
Alright, being forced to lane mid once because we had no one else suitable has changed my mind. I still think you shouldn't mid if you have someone better suited, such as Morgana, Karthus, Twisted Fate, ect, but Sona is the harassment queen. Her early damage is devastating to the poor sap middling against you. However, if you're against a hard pusher like Morgana or Janna holding mid will be difficult because Sona really can't push very well. I'll add some middling tips at the bottom later on.
Early Game: Grab your Meki Pendant, potions and get into lane with someone, preferably a hearty melee capable of first blood (Xin Zhao, Garen, Mordekaiser, Olaf, Pantheon, or Vlad are all excellent choices). However, before you leave the spawn, make sure to learn and use Hymn of Valor 3 times to charge her passive. Be wary of face checking bushes. If you're not sure if someone's there, don't go. You're so squishy it's insane. Now then, when your enemies appear, make sure to auto attack one of them with your passive, then start killing creeps. If the enemy gets close enough, blast them with Hymn of Valor. When you hit level two, learn Aria of Perseverance. This is to keep you and your lane mate in longer. If you play it smart, you'll almost never have to leave lane, and could possibly get first blood or a kill. Be very aware of mias, and place wards (or vision wards if there are stealth champs) in the bushes by the river, and in lane bushes. They're well worth the gold if they save you from a gank or get a kill for your team. Once you finish your boots, it should be about mid game...
Mid Game: Sona really shifts from a burst damager to support as the game goes on. You'll find your attacks do less and less...but they're far from useless. Harass enemies with your Q, and try to keep the W aura up at all times. E if you need to get somewhere fast or escape quickly. Stay back in team fights and spam your W to heal and Q to damage. You want to keep those auras up in team fights at all times. Remember to use your ultimate at the right times, to stun someone out of an ult (Nunu and Katarina come to mind), protect a fleeing ally, or stop a fleeing enemy. You should always be with someone, or else you're an easy gank target because of your frailty. Sona will be killed by any other champion 1v1 unless you're lucky or they're very stupid to not stun you and shut you down quickly.
Late Game: By now hopefully you have up to your Soul Shroud done. The game should be about over, but if not, it's basically the same as mid. Support, and keep those auras up. If your team is smart they'll protect you in team fights. If you win, gg, if not, you can't win em all.
Best of luck, and remember these are just guidelines. If you find something else that works, by all means change up my build and suite it to fit your needs. :)