Hey. I play AP Sona support a good chunk of the times I get autofilled support, and sometimes I even queue up for support just to play her.

AP Sona is the true pinnacle of bull. You have great healing power, poke, auto attack empowerment for yourself AND your team, nad you have an unblockable ult that keeps anyone in it still for at least a second. Sona is amazing in all team comps, and is a great support.

PROS:
-Good damage
-Fairly Mobile
-Good teamfight presence
-Single Target heal , AOE Shield
-Powerful ult

CONS:
-High mana costs early game
-Very team reliant
-Hard to come back from behind
-Will get focused hard
-Very high ult CD

Most of the time, you want to use your Q's ridiculous range to poke them down, followed up with an auto attack to get the extra damage from your Q AOE thing off. Your passive Q does massive damage, but shouldn't be used 24/7. Your W and E passives are also very good in lane, and I typically try to use them more, either to continue stacking damage, or stopping an enemy from doing any damage when my exhaust is down.

TL;DR, max Q first, then W, then E. Put an extra point in W if you're in a poke-heavy lane, or E if your ADC is low mobility and theirs is high.

Depending on the matchup, you're going to want to poke down the enemy ADC, and zone them off of CS, while your ADC farms for free. If their support has good CC (Thresh, Blitz, Alistar), play a bit more passive, and be ready to dodge abilities. If they have a healing support (Soraka, Nami, Taric), poke them down instead of the enemy ADC, to force them to use their heal on themselves, rather than the ADC.

When you're getting ganked, use your E, then empowered auto attack to slow either their jungler or the enemy ADC, making the gank much harder to actually finish.

You should always be with your team. Your waveclear is horrible and your utility is high, so stick with your team. During teamfights, you want to be positioned towards the backline, using a combination of your W and your Q to keep your team healthy, and their team not-so-healthy. Keep in mind that your Q gives your team an empowered auto attack, so try and get any AA based champs in it's radius.

Your ult can be used as a good engage, but an even better disengage. If your team has a better engage like a Syndra stun or Hecarim ult, save yours until it seems like you're going to lose the fight, then use it as a disengage and get your team out of there.

Lategame you should be playing pretty much the same as midgame, except now keep in mind that you do damage, and make use of that damage. When your heal is on CD, go for the enemy carries. Bonus points if it's a 2/19 Jhin. Be sure to not over extend, and think of yourself as a squishy zone mage, rather than a tanky 100-0 oneshot challenger smurf jesus christ how is this damage legal on a tank sona. You're squishy as the pillsbury doughboy, and should position as so.

Play AP Sona. She's seriously freelo right now because of the squishy mid/jg/adc meta. Blow up carries, aquire elo, and spam W.