I find Sona to be one of the most fun support characters to play for a support. Her heals, damage, and ultimate makes for a pretty good well rounded character. I prefer to play her as a very aggressive support, and if you do not, I am not sure this build will be all that great for you, or you might consider switching up the build order.

I prefer to build Ability Power runes where many people pick Gold/Sec runes for Sona support. The reason why I do this is because I find that paired with the the right masteries, you can gain that gold through poking and harassing which I will discuss later in the summary. The added AP gives you the ability to harass early on, and deal a decent amount of damage to your opponents. Finally, the added AP also gives you better heals to better support your lane mate.

I guess the most obvious thing in playing support is picking up all the masteries that give you gold. So make sure you get Greed, Wealth, and Pickpocket under the Utilities tree. I think that my favorite new thing in season 3 masteries for support is Pickpocket. This is a key thing for playing aggressive Sona. As I said before, the ability to pick up that gold through poking and harassing the enemy is key to being successful in getting your build up quickly enough, especially when you do not have Gold/Sec runes and when you do not build a Gold/Sec item right away. You also want to put some points into Awareness to up your experience gain. Finally, in Defense, build so you have increased health, armor, and magic resist. I also take 2 points in Unyielding for less damage taken by the enemy.

For items, I love Sightstone, Kage's Lucky Pick, Zeke's Herald, Shard of True Ice and Aegis of the Legion. This combo seems to give you to give you a lot of support auras for your team as well as give Sona the AP, mana and health pool that she needs to be successful. Sightstone is one of the best additions to Season 3, giving you wards, health, and the freedom to build more items, or have lots of wards to help your team with vision. I have found that buying lots of vision wards as well helps to maintain control of the river by Dragon and Baron, while taking away their ability to see. With Shard of True Ice, try to throw the active on your tank when entering a team fight, so that everyone is slowed. This can pair quite will with a Malphite ultimate, or any other move where the teammate jumps right into the middle of all of your opponents. Throw it on him either right before, or right after your teammate dives in. The other nice thing about the active on Shard of True Ice is that it has a relatively short cooldown.

I almost always pick up Hymn of Valor (Q) first, so you can poke right away with it. I only take heal [Aria of Perseverance (W)] first if someone on the team absolutely wants it. From there, alternate between Q and W through level 4. At level 5 take Song of Celerity (E) for the speed boost, but don't take another point in it until Q and W are maxed out. Obviously, take your Ultimate at level 6 and whenever you can. At level 7 I reverse my picking order on Q and W and continue to alternate because by that point your Q isn't hurting as bad as it did at first so therefore I favor the heal. If that is confusing, just look at my Ability order to see exactly what i mean.

When playing support bottom lane, I like to sit in the bottom bush and move in and out to harass. Run in and Q and auto attack once and run back. The key to this is making sure you know the range on Q to where it hits the enemy player rather than minions to effectively harass. The reason for the auto attack so to get the 3 gold from Pickpocket. If you do this constantly you can be very effective at damaging and getting gold.
By level 3 you should have placed your ward. If I have someone who is playing support from the bush the way I am, I place my ward in their bush to prevent them from doing so efficiently and be wary of early ganks. Otherwise, place it in the river to prevent those ganks. If the enemy puts a ward in my bush, I almost always put my ward in their bush to try to counter theirs and continue to poke. If you are hurting them enough and/or the minions are pushed up far enough move to their bush and continue to harass. Blitzcrank and Taric can make this a little more difficult, more so Blitzcrank. With Taric, just try to avoid getting stunned and you can do fine. Blitzcrank however, you need to ward their bush and continue to poke when you can, but be wary of the pull. The best thing to do is try to trick him in to using it but running up to just about where the end of his range is, giving him hope and get him to pull when you want him to and dodge it. At this point you have 15 seconds plus, to run up to him and do some damage. If you can successfully continue this, you will make him worthless assuming your ADC can keep from getting pulled. If he is doing well, simply keep your bushes warded and fight on the opposite side of the minions keeping the minions between you and him, and continue to poke when his pull is on cooldown. If you are on the purple side and have their ADC and/or support hugging the tower because they have low health, try to go to the other side and poke them, you would be surprised how easily the pressure from both sides and them having no where to go can pick up a kill or two. But be wary of the jungler or mid coming down to help, this has backfired on be before.

I love being in a lane with someone who has a large area of effect damage spell, like Miss Fortune's ultimate. Sona's ultimate paired with MF's ultimate can be downright deadly, so try to make your ultimate count when using it offensively. Even still it is great for engaging. If you think you can secure a kill with a flash and a stun, try it, it has worked well many times for me. Her ultimate is also very good for defense when running from the lane, ganks, under towers if they are pushing or trying to dive, or after a team fight your team has lost. The ultimate is also used well for team fight engages. I find it works quite well to use the ultimate after a few seconds into the fight allowing your team to do initial damage but them stunning them before they think they need to retreat. This however, is entirely dependent on how much damage output the other team has. You don't to use it later if your team is going to lose all their health in the process of you waiting, so try to be smart with it.

I hope this guide helps you. This build and strategy certainly works for me. Granted it takes practice to get it right. If you have questions, feel free to ask. Thanks, and see you on the field.