A valid question. Here's why you should play Sona

Sona has a ton of late game potential and AP scaling, and with the right skill, she can carry the entire game on her delicate shoulders.

Okay, but she's so squishy!

Yes, however her heal and aoe abilities MORE than make up for that. She can sustain, push lane, and carry an ally to safety with ease. We'll explain a bit more later, but for now, let's move on..

Pros

+ Strong Poke + Great heal + AoE Stun + Boots are Optional

Sona is great because she doesn't need potions to sustain lain. Her heal can keep herself and allies perfectly safe. Boots are optional with her. The magnificence of her e renders them useless late game. The simple fact that she has a stun makes her amazing, but the glory of an AoE stun? That's what makes Sona so overpowered. Plus dancing. Woot Woot.

Cons

- Super Squish - Relies on allies - Slow to start - Mana Reliant

As op as she might be, Sona actually needs a lot to succeed. She has low hp, armor, and magic resist. She also doesn't have a lot of mana to start with, making her heavily mana reliant until you can get some regen or extra mana. She's also relatively worthless without someone to apply the auras to. The passive just isn't worth much solo. Not to mention how hard it is to get her up to a decent ratio of effectiveness to mana. Which, lets face it, is gonna be your biggest problem with Sona.

Hymn of Valor

This is the first spell you'll want with Sona. The poke and aura of your q will be able to push back the enemy and help your adc give a few pokes as well. Early game, you'll want to keep poking with this and nothing more. Mid to late game, try to burst down a chunk of the enemy carry's health. This will either get your team a kill or push them off of your squishy allies.

Stats

Hymn of Valor deals a base of 160 Damage at max level, and it will scale with 50% of your AP. Not only this, but the aura will add 20% of your AP as a one-time buff for any allies in the area, causing their next auto attack to deal extra magic damage.

Aria of Perseverance

This should definitely be the second spell you get, or the first if you're wanting to play a bit more on the passive side of things. This WILL save your life when timed right. Don't be afraid to spam this during teamfights. A good tip is to w right after your adc goes in. They'll take a bit of damage, but your heal will fix that and the shield will negate the next auto attack or two.

Stats

Aria of Perseverance heals for 115 hp at max level, and it'll scale with 25% of your AP. The shield will last for 1.5 seconds at max level, and will shield for 130 hp. In addition, the shield will scale with 30% of your AP. This will save lives. During late game teamfights, tag as many allies as you can while still being safe. With enough mana and CDR, you can heal and shield about once every 3 seconds. Almost guaranteed win in every teamfight.

Song of Celerity

Song of Celerity applies a movement buff to yourself and allies, but it lasts longer on you. Low mana cost means you can effectively spam this to get into lane and to get out of a situation. I can't say how many times I've just barely saved myself or someone else just with e alone.

Stats

This causes her to gain and give 14% movement speed in an area at max level for 3 seconds. She can extend this buff by another 7 seconds (a total of 10 seconds to herself) if she doesn't take any damage in this time. For every 100 AP you have, the buff is increased by 6%. This gives it the ability to render any speed granting items useless late game, because with the bonus ap and low mana cost, you can spam this constantly to get everywhere. Don't be afraid to tag an ally with this if they're chasing or running away. Those 3 seconds of boost will surely make a huge difference.

Passive-Power Chord

I saved this for now because its effect depends on her other abilities. Every third spell cast gives Sona's next auto attack a special effect, plus dealing 235(at max level) extra damage that is increased by 20% of your ap. Lets go over the effects.

• Staccato will grant Sona's next auto attack its usual damage, plus an extra 40% damage. That's AD damage, mind you, but it DOES proc with her q's passive. Aka: Burst down all squishies.
  
• Diminuendo is guaranteed to save at least 1 life in every team fight. Do you ever find yourself playing against someone so overpowered you cant even handle it? Sona can fix that. When her w becomes her passive, her next auto attack will lower the targets damage output by 25%, PLUS an additional 4% per 100 AP for the next three seconds. You can take out a quarter of their damage on its own. With a lotta ap? You can easily take out at least a third of their damage output. Definitely try to hit the enemy carry with this.
  
• Tempo will guarantee a kill if the target is at low hp. Along with the extra damage, Tempo will slow the target by a base of 40%, plus 4% per 100 AP for 2 seconds. The slow will let your carry, or ANYONE really, catch up and nab that kill. It can also be used to run away. Spam e and when Tempo is up, auto attack and then e again to run away. More than half of the time, this will let you flee to safety.

Crescendo

Crescendo is Sona's trump card. An AoE stun that also deals some pretty good magic damage? Thats perfect! Just ult, and burst em down, then back up and let the adc handle the rest. (assuming they know that ult means "KILL") Also, it passively lowers the cooldown of all of her other abilities.

Stats

Crescendo deals a maximum of 350 base magic damage, and this will scale with 50% of your AP. Killer right? I might also mention that it lowers cooldown on her other abilities, that PAIRS WITH other sources of cooldown. This means that you can get a maximum of 40% cooldown from a max level ult, another 40% from items, and an extra 5% from masteries. All in all thats an 85% cooldown on ALL of her abilities. Basic abilities, I should mention. This bonus cdr does NOT affect Crescendo.

This is just a general summary of everything I've been saying throughout this guide, but let me get one thing straight...

SHARING IS CARING

Hymn of Valor, spread that dang damage buff! Aria of Perseverance, SHIELD YOUR SQUISHY SELF AND EVERYONE AROUND YOU!!! You need to run away or let someone chase someone down? FRIKKING TAG EM WITH SONG OF CELERITY!!! Sona is a decent support on her own, but the auras are what REALLY show off her skill. If you don't use them as much as you can, then why are you even playing Sona? It's not that hard either. Literally, 7 out of 10 times, you'll tag everyone when you use an ability in a team fight. Also, if you have everyone all together, remember this little HUGE tip...
Her auras will stack...
You heard me. You can give the buffs of all of your abilities to a teammate. There's an exception to this. Though. If you use and then use right after, Aria of Perseverance's aura will cancel out Hymn of Valor's. Aka, you can only have one aura active at a time. But once you give the aura's effect to an ally, you can use the next ability and it will grand them another buff. Simple, but a little mana consuming.

Stay cautious

Even with your strong heal and your e to run away, you can't always survive a situation if you get stunned. And trust me, when people notice you have the ability to carry, you WILL be focused. Stay behind allies, but still close enough to proc your spell effects. Granted, you'll still need to slide past them to burst down a squishy and then duck back in for protection, but that just takes a little practice.

Nab that Blue[icon=crest of insight size=50

Grabbing your blue buff when you can will help you stay in lane without having to go back as often, if at all. It makes your spells more spammable and gives you ultimate utility in game. However, should you decide that blue is needed, stay behind you allies. Once enemies see you have that buff, you WILL be focused more often to try and nab that buff from you.

Sona is a support carry

There's no denying it. With her late game potential and the items and runes to fit your play style, Sona can carry the rest of her team to a guaranteed win. Her teamfight potential is simply marvelous and will ALWAYS be a benefit, even if you lose the fight.

Some extra sappy stuff

So, this is my absolute first time making a guide on here. Or a guide for absolutely anything... I will GLADLY accept all reviews, comments, and questions, and do my best to respond as I can with the best information I can provide. Yeah, I'm only bronze 2, but I've mained Sona since I started playing back in 2013/2014. I'm not challenger tier or anything, but I do know a little about my Sona . Don't discredit me because of my rank. I won't do the same to you :)
ALSO PLEASE GIVE ME TIPS ON THIS BBCODE STUFF ITS CONFUSING AS HELL thank you have a nice day :3

Credit to jhoijhoi and everyone on his/her (not good with knowing genders..) guide. I used a bit of information from all of them and gave everything a try before settling on this design. Thank you!