Hey and welcome!
My name is Palshede, and this will be my second guide here on Mobafire.com, the first being my Olaf guide.

I have a top rating of 1447 elo on Europe Nordic & East and i have played a lot of support both in normal queue, solo/duoqueue and for my team.

And a few supports really stood out to me. One of them, Sona.
My Sona stats on ranked:
Sona offers poke in lane, sustain, a movespeed buff and damage.

So please, read a long :)

Pros

Good damage from a support
Utility
Sustain
CC on her ult
Brings something to teamfights
Movement Speed buff
Easy to get a hang on
Big boobs

Cons

As of the Shadow Isles Patch her base armor and HP is nerfed, alot. However she is still more than viable!
Not tanky
Can be picked off
Need to practice her ult to learn how to position yourself in fights

I have three difference rune setups for Sona.

First:My normal support runes, used on most of my supports. Gives gold, armor and MR. Pretty standard.

Second:
A little more offensive setup here, which I have found out to be pretty useful. Gives gold, armor, MR and AD. Your AA's will hurt a bit more, not intens damage, but pretty good early game harass.

Third:
Also a bit more offensive than the normal support runes. It has extra gold, armor, AP and magic pen. Your Hymn of Valor can be pretty hurtful with these runes, and can be deadly with your passive triggered on it.

The masteries i normal use for Sona are 0/9/21.In defense we have the extra armor, MR and HP.
In utility we have improvment on Flash, on range on wards, on move speed and most important the extra gold, both per time but also at the start + extra exp gain + CDR on Summoner Spells.

You could also use a more offensive page with 9/0/21.
In offense you should take either AP or AD, depending on your rune page, to complement each other as good as possible, also the CDR and improved Exhaust and lastly the one point in magic pen.

This is pretty much my core build as Sona.
When first getting used to Sona I suggest you start your build as this:
Start Faerie Charm and 4 Sight Ward + Health Potion.

But as soon as you are used to Sona, her powers, weakness, mana costs, cooldowns etc., I would say you should start:
Boots + 2 Sight Ward.
The Boots will help you poke, getting in and out fast and save, and since not many supports start Boots, they won't be able to help their AD trade. HOWEVER YOU ARE LOW ON WARDS!!! BEWARE!

Rush your Philosopher's Stone.

(And now Boots)

Next up you should go for the Heart of Gold, or even Kage's Lucky Pick for gold and small AP.

Cloth Armor. Will help you defend yourself in lane, and should be used later.

Boots:
If you see the chance of going Mobility Boots, i say "DO IT!". They'll help you roam, clear wards and place your own for vision.

Ionian Boots of Lucidity is another good pick, since it gives you extra much CDR and allows you to heal, move and damage much more.

If your botlane is getting hang out to dry Ninja Tabi for armor or even Mercury's Treads for the tenacity and MR.

You should try and see if you could afford an Aegis of the Legion it is a really nice aura item, giving you damage, armor, HP and MR + giving your nearby teammates the same things, although in a smaller package. Really, really good.

Kindlegem and Philosopher's Stone transforms into Shurelya's Battlesong. This item is always a nice pick up for the supports. It gives you HP, HP and mana regen, CDR + 40 % extra move speed in the active effect for 3 seconds. It can be used as both offensive and defensive, as a gap closer or a escape tool.

Warden's Mail with some more HP regen and armor and CDR. Plus it's passive with 20 % chance on being hit to slow the attacker's movement speed and attack speed for 35 % for 3 seconds.

Randuin's Omen is a mixture of Warden's Mail and Heart of Gold. Grants the same stats as the two build componants plus a really cool active. Slows movement speed and attack speed of nearby enemies for 35 % for 2 seconds + 0.5 seconds for each 100 armor and MR. Pretty neat in a teamfight to pop, to turn it around.

Zeke's Herald is the fifth and last item, wuuut? Yea. HP, CDR, attack speed and life steal. Oh did i mention that the attack speed and life steal is an aura for the whole team? Yea, it is.

Okay, only five items. Yes. You should always give yourself an itemslot for wards.
I didn't write this in, but remember to buy wards, at all times i suggest having atleast two on you.

And in lane, as soon as you see you and your AD having a lead, and you consider yourself save from death, consult your jungler and ask if you should get an Oracle's Elixir or if he should. If you get an early Oracle's Elixir i suggest getting Mobility Boots to roam and clear wards. If the game turns into pretty late game, replace Mobility Boots with either Tabi or Merc's.

ALWAYS GET WARDS!

Power Chord

- Passive
After casting 3 spells, Sona's next attack deals extra 8 + (10 × level) magic damage. This enhanced attack has an additional effect depending on which spell was cast last.

Hymn of Valor

- Q
STANCE – PERSISTENT AURA: Sona plays the Hymn of Valor, granting nearby allied champions bonus attack damage and ability power until she changes stances.

ATTACK DAMAGE & ABILITY POWER: 4 / 8 / 12 / 16 / 20
AURA DIAMETER: 2000
ACTIVATION: Sona sends out bolts of sound, dealing magic damage to the nearest two enemy champions or minions.

POWER CHORD - STACCATO: If this spell was last cast when Sona's Power Chord is ready, her next attack will double the damage of her Power Chord.
MAGIC DAMAGE: 50 / 100 / 150 / 200 / 250 (+ 70% AP)
TARGETING DIAMETER: 700

COOLDOWN: 7
COST: 45 / 50 / 55 / 60 / 65 mana

Aria of Perseverance

- W
STANCE – PERSISTENT AURA: Sona plays the Aria of Perseverance, granting nearby allied champions bonus armor and magic resistance until she changes stances.

ARMOR & MAGIC RESIST: 3 / 6 / 9 / 12 / 15
AURA DIAMETER: 2000
ACTIVATION: Sona sends out healing melodies, healing herself and the most-wounded nearby ally champion. Additionally, both Sona and the healed champion will receive additional armor and magic resist for 3 seconds.

POWER CHORD - DIMINUENDO: If this spell was last cast when Sona's Power Chord is ready, her next attack will debuff the target to deal 20% less damage for 4 seconds.
HEAL: 40 / 60 / 80 / 100 / 120 (+ 25% AP)
BONUS ARMOR AND MAGIC RESIST: 8 / 11 / 14 / 17 / 20
TARGETING DIAMETER: 1000

COOLDOWN: 7
COST: 60 / 65 / 70 / 75 / 80 mana

Song of Celerity

- E
STANCE – PERSISTENT AURA: Sona plays the Song of Celerity, granting nearby allied champions bonus flat movement speed until she changes stances.

MOVEMENT SPEED: 4 / 8 / 12 / 16 / 20
AURA DIAMETER: 2000
ACTIVATION: Sona energizes nearby allies with an additional burst of speed for 1.5 seconds.

POWER CHORD - TEMPO: If this spell was last cast when Sona's Power Chord is ready, her next attack will slow the target by 40% for 2 seconds.
BONUS MOVEMENT SPEED: 6% / 8% / 10% / 12% / 14%
TARGETING DIAMETER: 1000

COOLDOWN: 7
COST: 65 mana

Crescendo

- Ultimate
ACTIVE: Sona plays her ultimate chord in a broad line in front of her, forcing enemy champions caught to dance stunned for 1.5 seconds and take magic damage upon impact.
MAGIC DAMAGE: 150 / 250 / 350 (+ 80% AP)

RANGE: 1000
COOLDOWN: 140 / 120 / 100
COST: 100 / 150 / 200 mana

I like to max my Q first since it brings a lot of damage, AD and AP to the table. Makes you and your team so much stronger. This is the Sona poke, a Q followed by the passive Power Chord hurts a whole lot on the fragile AD Carry.
I tend to pick Hymn of Valor while in base and use it three times so i have my passive triggered and ready to be used if your team or the enemy team decides to invade.

BEWARE, YOU COULD WASTE YOUR PASSIVE ON WARDS, WHICH DOESN'T GIVE EXTRA DAMAGE

After Q, i max W. This is Sona's heal, and this allows her and the AD Carry to stay in lane much longer than a no sustain lane. Always useful.

Lastly i max E. Sona's E gives small move speed bonus passivly and after activating a bit bigger move speed bonus.

The ultimate Crescendo is so, so, so good! It's a 1.5 seconds stun AND IT MAKES ENEMY CHAMPIONS DANCE!!! WOW. So useful winning small scrimages and big fights, because this allows your team to focus one down fast and safe.
Pick Crescendo whenever you can.

Flash and Exhaust.
Flash is standard, most used summoner right now, and really good. No need to introduce.

Exhaust is deadly. It has a built-in slow, 40 % movement speed, and makes the champion weaker, attack damage is reduced by 70 % and AP is reduced by 35 % all of this for 2.5 seconds.
And with the mastery in the offensive tree, it also reduces MR and armor by 10 on the enemy. It's relly good to soften someone up.

Green circle: these circles indicates good and simple places to ward. By buffs, i only showed the enemy red and blue, but you should also ward your own buffs. These placements gives great vision through out the whole game, however during lane it's not your job to ward top and mid.
Red circle: gives vision over Baron and Dragon, so your team have information on whether they are being taken or someone is warding there and so on. I suggest you pink ward these places.

1:
If the enemy picks champions with healing reduction Sona is not a safe pick, since they can reduce her healing

2:
Seeing the enemy team picking Blitzcrank or Leona as supports, dont go Sona. They both can pick her out solo. Blitz can hook her and Leona will Zenith Blade to her and after one Q-E combo from Blitz + damage from his Carry Sona is dead, the same with Leona. If she hits Zenith Blade (E) on Sona and follows it up with Shield of Daybreak (Q) Sona is vunerable as hell, and will

3:
Tenacity:
If the enemy stacks Tenacity (and has Cleanse) renders you and your ultimate pretty useless.
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Sona is an easy support champion, which offers a lot of things, and can turn the tides on Summoners Rift.
Although being nerfed like crazy in the Shadow Isles Patch she is still viable and can be really strong in the botlane, because with her skillset she synergizes well with pretty much every AD Carry.