Alright, So since you asked in another thread, here's a bit on Sona's paly style.
I've been playing Sona since season 3, for the current season she is my most played champion at 112 games. Currently I'm sitting at an average 5.55:1 KDA with her. I play her as a support in ranked but I have played her mid and jungle in normals. I typically take flash exhaust but ignite is also viable, though it doesn't scale as well into the late game.
Sona is a poke mage with some healing. She might have the best laning phase of any aggressive support in the game, being quite a lane bully especially in some match ups.
At the start of the game you should get 1-2 stacks of your passive ready in the base, depending on where your jungler starts, if you will be leashing and if you want to burn a bit of mana on the leash, you should get into lane with 2 stacks, so you can help push for an early level 2 without wasting the passive and also auto-Q-auto the enemy as soon as they enter the lane to get an early health advantage.
As Sona you should be looking to utilize a hit and run style in the laning phase, when an enemy comes up to last hit, you harass them with a Q combo, there are 4 ways you can do this depending on your passive charges and the range you are able to move into safely, if they are at 0-1 Q then auto to proc the on hit damage, 2 stacks you will auto-Q-auto as your passive is an auto attack reset and will allow you to proc the on hit and the passive damage as well as land an extra auto attack, at 3 stacks you Q then auto. If you are not in range to land an auto you can still harass with Q alone as the damage is fairly good. You want to avoid taking damage as you are squishy and heal costs 80 mana with one point in the ability, staying at high health also makes you less likely to get jumped on.
You can also look to roam once you have your ultimate, this combined with either the burst from Q or the slow from E usually results in either a kill or blown summoners, either way relieving pressure from the lane, typically you can roam mid, but roaming top after basing is also an option.
In team fights you will either want to be peeling for your carries or assisting with chasing down the enemy carries depending on the comps. keeping tempo available is great for either situation as the 40% slow will assist greatly with kiting and if you had it charged already you can cycle your abilities for a second charge quickly to get a 4 second slow. for high damage burst champions or DOT based enemies you should usually keep diminuendo up, this works on top of exhaust and combined with the shield, heal and an AOE stun you can make someone extremely difficult to kill.
Late game Sona is a utility mage, items like
are great pick ups, though high AP items can also be great on her as her abilities all scale with AP, an early
can be later upgraded into an
for a late game boost to all of your abilities. She can also be played for damage, though not as consistent a source of damage as some other mages she can excel in poke and siege comps, or vs teams without much pick potential, in this case
can be a viable choice mid game after getting
and a gold item.
can also be an interesting pickup on her as you could combine it with tempo to keep an enemy slowed for even longer, or use it to improve her kiting potential outside of situations where tempo is the best choice of passive.