Hello, My name is Troy "Don Schnitzel II", I'm currently a plat 4 EUW support player. I figured I'd write a Sona guide for a potential support player, although Sona is very difficult to play it has a high potential in the late game. Thats why I'll help you through the early & mid game as much as possible. ^^
This is also my first guide, so I'll work on syntax/smooth it out a bit more later.

Marks: substitute for armor seals (flat armor)
Seals: Health per level so you scale better into midgame/lategame.
Glyphs: scaling MR so you dont get one shot by brands/zyras/leblancs

Quints: players choice, I like gold best. But if you eat alot of harass, extra defence might also be good. Flat health regen/armor/flat health might be good aswell.
if you are confident you could change into AP, however i dislike poke on sona due to the fact that you're already very squishy, so you're putting yourself in useless amounts of risks.

Pros:
1 Ridiculous healing/utility mid to late game with ardent censer.
2 Good team amplification due to speed from your E & W shields.
3 Gives team someone to swarm around (core of the team).
4 Late game monster.

cons:
1 Really difficult early game.
2 Squishy.
3 Wont be effective untill you atleast buy 1 health power item.
4 Other champs might do what sona does better.
5 If you're caught by any hook/hard CC, you're dead.

Eye of the oasis + boots will be your support core, you'll always rush this, no matter what.

options
Redemption: Buy this if your group teamfights early, it scales well with your natural ability & gives you an ability to save someone even if you're far away. This is a really good item to rush as second item. But if your team is laning longer, Ardent Censer might be a better option. But if teamfights occur, redemption is the better option. redemption will also proc(activate) any spell effects (I.E: ardent censer/rylais)

Ardent Censer: Scales ultra well with you since you can proc it with your W. buy this in your core, Runaans procs this effect 3x every auto attack. So at lvl 15~ your adc will heal an extra 100 per shot which is a massive amount considering the effect stays for 6 seconds & an adc has an avarage of 1.5 attack speed. That means your adc will heal approx 900 health, from 1 W. plus will deal an extra 900 damage total over the span of 6 seconds. which is absolutely huge. you can proc this on everyone so everyone gets the healing/attackspeed/magic damage which makes sona such a great champ to buy this on. an absolute must buy

micheals crucible: Gives you 20% healing power, extra hp regen, MR, mana regen, and a cleanse. This cleanse can be used on everyone (I favor it on front liners so they seem more threatening. But you can use it on adc's aswell. In my experience adc's die too fast to be used on (nuked).

Locket of the Iron Solari: Good brace yourself item, scales with healing/shield % power. so highly effective. cant be used under heavy CC (counts for all items but you need to see the engage comming.

Zekes Harbinger: Good amplifier for your adc, best buy on adc's like Jinx/Caitlyn/Jhin/Tristana/Ashe. Basic autoattack based adc's that use either the crit well or buy runaans.

Lich Bane: Good poke/dmg item, but its relatively useless in the build I recommend

Athenes Unholy Grail: Utilises poke too much to be effective over michaels. But if you're doing damage sure why not.

Rightious Glory: If you need that charge mentality Kled offers, but dont have a Kled cause hes drinking mushroom juice somewhere else.

Trinkets

Farsight totem vs Oracle alteration

Generally Farsight totem is a really good option if you're winning or if you're up against assassins.
If you're winning, use farsights to place defensive wards (they wont run out & you'll notice where the enemy breached your jungle. It'll also give a sense of safety to your team having all that vision in your own jungle.

If you're against assassins you're using this whenever your team is clumped together and invading hostile teritory (say jungle brushes). Put them at choke points so you can figure out where the enemy is scattered & then clean them up



oracle alteration: tho its good for clearing and offers your team the ability to deny vision, because of your squishiness its a bad pick, you shouldn't be the one carrying this, a tank/juggernaut should. convince your top/jungler to pick oracles whilst you can take the farsight.

2 ways to play

The "Janna" way, and the rundown CC way. (interchangeable aswell)

the "Janna way"

Position yourself so that you put your frontliners (bruisers/juggernauts) between you and the enemy, you want to be able to hit most people with your W, and E.
Save your ult for assassins/engage juggernauts that go on your backline. use your E powerchord to slow down any juggernauts that break through your front line.

The rundown CC way follows after the enemy comp breaks & they try to regroup, basically slow them down as much as possible so your team can devour them alive.

You have coin, just avoid jungle & play alot around your team.

If your adc sucks & dies twice, and you cant stay in lane, then abandon ship.
Roam and hope mid/jungle/top carries.
(This will tilt your adc alot so it's recommended you tell him to follow you, if he calls you a noob. DONT flame him cause in the end it'll just put more fuel to his toxic behavoir. Just ignore, plead that he joins the team and try to keep him alive as a low priority peeling target)

Your biggest concern early/midgame is your teams mentality, since you're a late game monster, early game doesnt really do well for you. So you need to put up wards, praise people & micromanage them like the little kids they are (Cause lets face it, aside from babysitting you can't do much else) If your team tilts before minute 20 you automatically lose your chance to scale. Which makes you a target for flame & salt.

Your biggest goal throughout the game, is avoiding risks. and making sure any risks the team makes pay off.

Okay kids, lets talk about wards.

First off, lets establish some catagory wards

Laning phase wards, Agressive wards, Invasive wards, Defensive wards, Chokepoint wards.
okay, now lets begin

Laning phase wards: This is gonna be your warding style till whenever the adc says lets roam or you're forced to roam, you want to keep track of your Tribush on both sides, for purple side use a control ward, for blue side only a control ward if you have lane dominance.

Place a ward, in river brush (since the plant can just launch them into it.) and use a ward in whichever bush they try to occupy to avoid lane ganks. You can also put a ward over their at their jump plant to pop it with your autoattack denying them the time. But only do this if you're confident you wont get wrecked in the river.

Agressive wards These are wards that are set with minor to great risk. such as an enemy buff ward, jungle wards. and generally risky wards. You can set them if you're sure you're not in danger, use stealth wards from your sightstone/warding trinket, never use farsights for this cause they'll guaranteedly get cleared.

Invasive wards These are wards that open up invasive options (such as a buff steal, or a gank. theyre best set around buffs & the bushes behind midlane T1 tower.

Defensive wards These are post laning phase wards that protect your jungle, the best to use for these are farsight/control wards, cause they dont expire. if your control ward is being cleared, try to contest it, ping as hard as hell
The best places for these wards are jungle entrances & jungle brushes of the "allied teritory jungle"

Choke point wards These are wards set to provide optimal view in a choke point, if you can set this up you can try to lure the enemy in. best around red buff or the midlane - dragon river brush, or blue buff intersection that goes into a +.


okay, now that we discussed each warding type, theres also one extra catagory.

Improvisation wards
These wards are perhaps the most important that you'll set, they are set during fights to allow vision on the enemy so that your adc/team can actively autoattack from range & aim better. If you dont set these during teamfights you're a bad support. because you deny your team the damage they could potentially do, and force them to risk facechecking certain areas which brings them in danger, call it counter supportive play.
SO! these wards take priority above all wards, make sure you have atleast 2 stealth wards during each team fight