Sona, My Understanding
This is my method of playing support Sona and my observations of her strengths and weaknesses. I hope people find it helpful both in playing her and playing against her.
Sona is a champion with a huge potential to bully in lane and grants massive amount of damage to her team in the form of a support. She has a little bit of everything for CC but mostly for single targets except with her ult. She has a very strong laning phase and strong late game but her mid game is her weakest point.
Power Spikes
Sona has a huge early power spike at level 3 in which her poke becomes a huge hindrance to the enemy duo.
Sona should be looking for plays after level 6 to make use of her ult as it can be game changing.
Sona hits another power spike with
built as she also gains that 50% crit, 20%ap and with a passive Q shot that can really hurt the target a lot if it crits.
gives her a huge power spike in helping her team take objectives.
Laning Phase
Start:

Sona is a lane bully. This means she creates a lot of pressure on the enemy team by dealing them damage by poking. However, she is actually really weak at this at level 1 and 2 because 1 point into Q only grants 40 +20 magic damage to one target (when only she is poking). Even with an empowered Q passive it will only bring the damage near what the enemy can return with a similar spell. For instance Lulu Q level 1 does 80 magic damage. You get 40 magic if you only hit with Q active. If you go in for an AA the enemy will also AA you back, you get only 20 extra damage +19-36 (level 1-2 with Q proc) magic damage if the passive is triggered. As Sona is pretty squishy this trade often ends up worse for Sona. Level 1 you will deal less damage, level 2 you come out about even. The first 2 levels is where Sona can fall behind and have trouble poking thereafter if she took too much damage. My advice is to just hit them with Q active and Q passive proc'ed AA only and only if you can do so safely (enemy cd down).
Level 3 is where you turn up the pain. Spam that Q for 80 +30 with aa magic damage now and your passive has finally added up to a point where the enemy duo can't really out poke you with their abilities compared to yours. Sona doesn't need to use her AA with every cast. It is fine to just hit with Q active as Q is very efficient for it's cost. You don't need to kill the enemy you just need to push them off CS. If they have to back to heal up you did your job as Sona. This can (not always) quickly lead up to a 10-20 cs lead for your ADC by level 5. You want to be casting Q a lot not only to bully the enemy duo but to also proc spell thief which is ridiculously easy with Sona.
W is a trap at early levels. DON'T use it unless you have to! It is not meant to sustain the lane but rather save your ADC. W cost 80 mana at level 1. It will only heal your ADC for 30ish hp! That is a really low amount for 80 mana and not useful for sustain in anyway. Instead when your adc is low and the enemy tries to go in for that snipe cast it to heal for closer to 45 and shield for 35. If you have full or mostly full mana feel free to cast it once or twice but do not spam it. If you take a bit too much damage eat a biscuit instead of casting W unless you have excess mana. W will have a place later but for now it's kind of worthless.
Early Shopping
first buy. Always. You have no escape so warding well around your lane is super important! I like to ward the small river bush, in front of dragon pit and one of the bushes in lane. However, If we are heavily pressuring the enemy duo (which othen happens with Sona) I will place ward between enemy blue buff and the toad instead of in front of dragon pit.
I try to get one of these with my SS as Sona is so good at keeping pressure on the enemy duo that you can often keep it until the enemy jungler finds it (your already long gone so he takes it as a consolation prize). I like the tri bush(blue side) or large river bush(if red side), or the bush next to our red (if blue side) or the bush between the river and blue(if red side).
Item is a must as it give you armor and mana two things that Sona gains a lot from. Throw in CDR and it is really nice.
Take your pick of boots really. I like Soc Boots to increase my dps but Mobi is great for roaming and lucidity for a burst of CDR if we are falling behind.
Never upgrade this. It is worthless to upgrade. You want to start with it but you will never need to upgrade it.
Mid Game
This is where Sona can really struggle. From levels 8-12 she has a serious lack of power because her poke is great but in a teamfight you can't just go poking the enemy whenever you want (unless you want to get blown up). W is still too weak to be of much use. E can be useful but only in a minor way. If you didn't snowball your lane you are going to find you have little impact on the game if you cannot land a good R. However, you can itemize to minimize your uselessness in midgame. Right now your biggest contribution is damage. You don't have sustain and you don't have the best CC (you do have some which you will highly focus).
What you need for to get through midgame:
First
is your key item to get through midgame. you are going to pop this bad boy's active on your team's carry. This is hopefully your ADC but it can also be your ap mid (20% bonus ap goes a long way). You will then stick with them as best you can. Hopefully they are not looking to split push as you will not be doing that. You want to stick with your team as you scale with the number of allies you tag with auras.
Second
to build this as the second item on your team ask yourself; do you have a protect the adc comp, all ad team, or a low damage team in general? If the answer is yes to any of those get this. This will greatly increase your team's magic damage output preventing enemy teams from building
and
to try and capitalize on punishing a team that is heavily AD focused for damage. Between Sona Q and Ardent procs your team will be dealing more then enough magic damage. This item is insanely effective on Sona because W can easily shield everyone on your team.
or
build this as second item if the enemy team has an AP carry that is snowballing or if the enemy team has multiple sources of AP damage. This is also great to build if the enemy team is always grouping and doesn't have a good split pusher.
When to CC:
You have two forms of non-ult CC, a W passive and an E passive. Use W passive to tag enemy assassin's to prevent a good chunk of their damage. Use E passive to peel away enemies trying to get to your carry (whoever is Zeked). You should have one or the other at the ready so a green or purple ring should be floating around Sona at this time. This is because you can quick cast all three Auras again to get your passive right after using the passive. Make sure that when you do this that you wait for your AA to hit and apply the passive and don't cast an aura before the AA hits or you won't get the second passive proc.
E proc is particularly helpful in lane. If you have a purple ring around you the enemy duo better beware because you can slow them and then quickly proc a second passive to either slow again or deal some serious damage. E proc is great for when the jungler is coming in and can be pretty good peel at early levels against the right targets. I highly recommend having a purple ring up every time you return to lane after buying and getting another purple ring up after you used a couple Qs as long as you are above 50% mana.
R has two uses. It can be a very powerful form of peel or it can be used to engage. There are so many variation on when to do one or the other that it would be another super long post just to explain. Just keep in mind that when you use it, use it at the right time. It is perfectly okay to hold onto it a bit instead of just casting it on impulse. This will take practice and an understanding of how other champions work together to really grasp when and where to ult as Sona.
Late Game
Sona is amazing in the late game, when she has
she brings so much damage to the team that is is amazing. She already often has the highest damage for a support in the score screen and often outstrips other roles for damage. However, this damage isn't calculating the procs granted to allies from her Q or the ardent censor (that's added to your allies score). This also doesn't calculate the damage granted from allies getting 15% increase AS. You bring so much damage to the table that you are kind of like another carry but in support form so as long as you have a pair of tank alive with you you can still deal some serious damage.
Late game is all about positioning for Sona. She likes to be in the middle of her team which can make her a target to certain champions that excel at diving. This can also be dangerous against Wombo teams so make sure your team is spread out but easily taggable (its an art). She will be highly mobile with a maxed out E allowing her to move around easily and get good angles for her Ult or just to kite back and Q poke. Try to shield as many in your team as possible with W and tag as many as possible with her Q. Sona wants to stick with the largest part of her team and likes to be with her entire team when able. You are almost as big a threat as your carries are so keep that in mind as you make a nice juicy target for assassins.
Make sure to keep wards up, if you don't have 3 on the map place one! Even if its not the optimal place. If you are in a game where you're the only one warding (despite those amazing trinkets all your allies have) focus your wards in an area that you and your team can use as an escape or spot a flank coming. Don't spread them out everywhere get 1/4 of the jungle favorable to you and your team and make sure they understand that is their escape route (so protect it!). That way if you need to run or kite back you don't have to worry about surprises in the bush.
When to pick
Alright, so now you know her strengths and weaknesses so when do you pick Sona?
Teams-Comps/opponents Sona likes
TEAMS Wombo Combo teams Protect the ADC teams AD heavy Teams Objective Focus Teams (ones that take neutral objectives quickly)
ENEMIES When against a team with no assassins. When the enemy bot lane has short range (vayne, sivir, graves...etc) When the enemy bot lane has no or little sustain Kiteable enemies
Teams-Comps/opponents Sona hates
TEAMS Poke team Heavy AP team Sieging Team 1/3/1 team
ENEMIES Pick Heavy CC (Blitzcrank, Morgana...etc) (can't do much with a dead ADC) Good Dive Assassins (Zed, LeBlanc, ...etc) Heavy Sustain (Soraka, Alistar, Draven with Vamp...etc) Strong Zone Control (Azir, Zyra, Heimerdinger...etc)
Sona can be played with or against any of these but she will have far more impact when she is with a team that can utilize her Auras to the fullest. The only true counter I've found for Sona is Soraka because she completely nullifies Sona's early game and has a strong impact late game just like Sona but heals for just as much damage as Sona brings to the table and then some. (Unless I flash ult kill her because she went down to 1/2 life from healing :P)
I hope you all enjoyed my take on how to play Sona. If you have any questions feel free to ask.
for double the gold generation. It has more than paid for itself by the time I sell it to get a final item. I never go to tier 3 though.