Of all the enchanters that exist in game, Sona is the best and easiest to play. However we need to be mindful of her weaknesses. And to start we need to talk about her W and her manapool.

Sona's mana pool at level two -- where you level your W -- is going to be no more than 373, and if you been a good Sona and have been poking the ever loving **** out of your enemy laners, it's going to be somewhere around 500. You desperately need that Tier of the Goddess in order to be able to function without worry and needing to constantly back to base or rely on your ADC to not get hit by anything because them getting hit means that you will go oom (out of mana)faster.

When in laning faze you must realize that there is only one thing you need to do but it's easy to **** up. You need to get close enough to get your Q and autos off onto the enemy laners and the weave back to your ADC and avoid getting poked. You need to make sure and pick your targets wisely. Most of the time you are going to have to hit the enemy Support however if they out-range you or are anything that can CC you with the slightest of ease or stay out of your range, you need to aim for the ADC. If you can constantly hit both, then do so and focus on the one that gets chunked down the easiest.

Your first back REQUIRES AND DEMANDS that you get a tier and focus on building Archangels Staff first! You need to do so to because it's the only thing that will save you and your ADC from losing trades and not being able to heal the damage that will be dealt to you.

Use your E to increase your Movement speed so you can get close to the enemy to poke them and then go back to your ADC before the enemy can do too much damage to you. Once you get your Ulti you need to start looking for plays. Poke them down till they're at around 50% to 25% of their health and damn near 3-shot range. Once you get them there you should be able to flash into them and your ADC can follow up and get a kill.

However, as Sona you are going to have to make sure that your teammates are aware enough to follow up on your aggressive plays. Your poke, your stuns, your slows, and such. If they routinely don't then you are screwed and there is nothing you can do about it. "Sup difference" doesn't matter, what matters is "Team difference".
Lower Elos are notorious for having the map awareness of a corpse and they will not be able to handle an enchanter like Sona, they don't know how to follow up your stuns and poke and will just completely ignore your efforts. If you are dealing with a team that is ignoring your efforts in an Elo where enchanters are viable, then you need to build burst.
If you are in such a situation build things like Ludens, Deathcap, and whatever whatever it is that you think will work depending on your situation. Upon getting your build go for picks on the squishiest of targets you can find. Ensure they are alone and their allies are distracted, pay attention to the situation and evaluate what will work and what wont. Remember, it's all about critical thinking and knowing when to go in.

Sona plays aren't flashy majority of the time and they rarely will be. The flashiest thing you can do is a flash ult Q power-chord combo. In which you flash into the face of the target, Ult them, use your Q and the auto them with the Q empowered Power-Chord fully stacked Empowered Auto Attack. This should, depending on how far you are into your build, and what you build, deal enough damage to at the very least deal anywhere between 25% to 50% of their health. If you're going Full AP then they should be chunked as if they were dealing with an Annie. If you're going Hybrid Sup/AP build which is the main build, then they should have at least 25% of their health gone.

Make sure you target the squishest members of the enemy team, and the ones whom dive your carries. For example:

If a Zed ults your ADC and doesn't have a means of escape, ult him and then use your Q Power-Chord Combo so that way you can turn that dive of his into a mistake. BUT this requires extremely precise timing and practiced execution. It's a roll of the dice but a Sona that can pull it off is a Sona that will turn an entire game around.