Before leaving base, prepare Power Chord. By the time you get to lane, go near the enemy carry, and chain Hymn of Valor and a basic attack IMMEDIATELY. Doing so will chunk them for a substantial amount of health.
Sona'sHymn of Valor is very strong if leveled up quickly. This is especially good if planning on going as a poking support.
In a passive support lane, encourage your carry to trade blows with the opponent, as using both your Hymn of Valor and Aria of Perseverance lets the both of you make easy and effective winning trades. However, do not spam the heal too much, as it is very costly during the early-game.
Use Aria of Perseverance when an ally is being focused in order to take advantage of the aura's shield.
Stay with your team. Sona's auras are most effective when the team groups up. Sona makes an excellent healer, Crescendo is best used when the whole team can take advantage of it, and Song of Celerity lets the entire team kite. Without a teammate around, Sona is little more than an easy gank.
Early game, be wary of constant spell rotation, as it will quickly drain her mana. However, this can also be a large problem mid to late game without proper itemization.
Crescendo is a powerful CC that can stun an entire team. Strive not to waste it, use it to counter-engage for the highest chance of success.
Flash can be used to quickly reposition for a maximum target Crescendo.
Being a support, Sona should focus on supporting her AD carry early game by warding and keeping them safe. This means getting by with less gold and building so as to benefit your team.
Your ideal support item is Spellthief's Edge. Your natural playstyle focuses on harass, and this greatly complements the damage output with an easy method of gold generation.
Ancient Coin is also quite beneficial, as you can safely sustain and create a passive laning environment that zones out the enemy.
Getting a Chalice of Harmony in the early game is beneficial as it provides some magic resist as well as enough mana regeneration to spam abilities in lane.
Sheen is a situational item. It works really well with all of Sona's abilities, and it becomes more of a threat once it is converted into a Lich Bane.
Aura items are available that benefit Sona's playstyle.
Frozen Heart's debuff to enemies' attack speed decreases the DPS of auto attacks from the enemy team while giving you more CDR and armor.
Abyssal Mask's debuff to enemies' magic resist increases the magic damage output of your team while giving you more magic resist and health.
Mikael's Crucible is a powerful item because it's capable of saving an important teammate, letting them continue fighting by removing CC. The massive mana regeneration is also useful.
All of Sona's abilities (including her passive) scale with AP, but support Sona should prioritize CDR over AP as to maximize the utility of her abilities and passive.
Sona is extremely valuable in teamfights and group pushes, but sustained aura rotation can deplete her mana pool quickly if not equipped properly. Use any available mana sources to extend the duration of your presence on the battle field.
Sona'sAria of Perseverance can shield multiple allies at once. This makes Ardent Censer a very good item on her, providing a slew of useful stats alongside an attack speed and magic damage buff for allies which, no matter the composition, will improve her team's objective taking. Also, you can further extend the duration of Ardent Censer's buff on a single most wounded nearby ally by approaching them no more than 3 seconds after activating Aria of Perseverance, thus refreshing Ardent Censer's buff's duration for up to 9 seconds total.
Sona is fairly squishy throughout the game, especially at level 1. Work with your allies to kill her fast.
Just be careful not to give her the upper hand through your aggressiveness. Being a support, her allies are her main survivability, and making the mistake in ignoring them can prove to be more fatal than ignoring Sona.
Constantly try to harass Sona and her lane partner. Doing so forces her to use Aria of Perseverance, and it takes up a lot of mana in the early game.
When laning against Sona, remember how she can boost her partner with her supporting spells. When focusing either of them, you're really going to be fighting both of them, so account for it by removing either from the equation with CC or zoning.
Sona's harass is targeted, which means that to avoid her damage, you need to either block the damage or not be there to take it in the first place.
Hymn of Valor cannot auto-target enemies not in vision, so take advantage of brush and control vision.
Do not overextend when chasing an enemy that is accompanied with Sona. Her Song of Celerity allows her to outrun you very quickly.
Sona is a rewarding target to remove quickly from the fight. If the opportunity presents itself, remove her from the equation.
Avoid grouping against a Sona. She can end up hitting all members of your team with Crescendo.
Sona is best countered by using an aggressive support with heavy CC, such as Blitzcrank, Thresh, or Leona. Keep in mind that you must play very aggressively against Sona and not give her time to recover her spells; otherwise she will just end up harassing and out sustaining your aggressor of choice.
Alternatively, using a support with similar healing and harass, such as Nami or Soraka, can be a good choice for stalling the lane and at least not letting the enemy snowball.