Long story short, you are a support character. But Riot feels the need to give you some incredible damage output, so why not use it in a way that blends support and damage.

Top Choices:

CV and Flash are the two summoner skills recommended in the summoner spotlight, which I whole heartedly agree with.
Clairvoyance - Map awareness is key.
Flash - Can help you get out of a tight bind.

Substitutes include:

Clarity - If you find yourself always running out of mana this can sub in for CV, but mana shouldn't be too much of an issue.
Cleanse - In ranked play, if you notice a lot of CC, you can grab cleanse just to be safe. In normal games you don't know who you are going up against, but could still be useful.
Fortify - Always a good spell. Could give your team the extra 8 secs they need to get to a tower, or stop a certain BD champ.
Ghost - Song of celerity is not enough to run away. Use this if you are not comfortable with flash.
Heal - What's more annoying than a healer with heal? Seriously, what?

Maybes:

Exhaust - Could be used to help your carry get a kill, help you escape from a single pursuer, or reduce the damage of an ulting Kat/Nunu/Tryn/etc., but really thats why you have your ult, and possibly a green Power Chord, so this spell isn't really that useful.
Teleport - If you are teleporting to a tower in distress, you alone probably won't be able to do much, although it can be used to get back to your lane quickly or to catch up to your team.

Never take:

Ignite - No stealing kills from carries.
Rally - Not worth it, but most people already know that. Also, you shouldn't be far enough up the offense tree to get improved rally making it completely useless to you, as opposed to just useless.
Revive - If you just like being annoying to the enemy grab this spell, but as a support character, you should be in the back, supporting, not tanking the enemy.
Smite - What are you doing in the jungle?

I've found using mana regen per level seals combined with masteries and items will leave you with enough mana so that you can keep using spells at a reasonable rate.
I can't recommend any other seals.

Not much to gain from marks, so i recommend the traditional magic pen.

For Glyphs you have some freedom of choice. The available choices are:
Flat CD
Flat AP
AP/Lvl
MR/Lvl
This is all personal preference.
For more spells in a shorter time, CD is the way to go.
For bigger heals early on, flat AP.
Later on, AP/Lvl.
if you find you really enjoy spamming spells, but don't want clarity, MR/Lvl.

Quintessence follow the same path as glyphs, but I recommend Flat AP to give you that extra damage and heals early on.

Your passive, power chord, does damage and a bonus effect based on the last spell you used before auto attacking. For that reason it is important to watch your aura when power chord is ready.

Hymn of Valor, put a point in it at lvl one then let it sit until the end.

Aria of Perseverance, max quick as this will be used to keep you and your team alive.

Song of Celerity, Max second as this will speed up pushing, allow you to kite in and out of battle, and it speeds up minions which are adorable to see scurrying into battle.

Crescendo, Your ult... Get used to it, it will allow to to save a teammates life or doom the enemy team by making them dance in place.

Start off with Mana Manipulator or Meki Pendant depending on your lane mate.
or
Mejai's if your comfortable.

Go back when you can afford a philosopher's stone.

Shurelya's Reverie + Soul Shroud + Masteries = 34% cooldown reduction.

Kindlegem is pretty much your core item as it builds into two of my recommended items.

Boots of Swiftness/Ionian Boots of Lucidity/Mercury's Treads/Sorcerer's Shoes

Boots are always a by-game decision.

There are four distinct possibility and all serve a different role, but the shoes needed to get the gob done is determined by both teams champion composition.



If you want to kite really well, Boots of Swiftness allow you to run in and out of battle with ease.

If you drop Soul Shroud or Shurelya's Reverie, I recommend these boots to put you over the 30% CD reduction mark.

Notice a lot of CC? Grab yourself some Mercury's Treads.

If your team is lacking in AP, or you want to play more offensively, Sorcerer's Shoes will make your spells hit a bit harder.

Doran's Ring
Abyssal Scepter
Rod of Ages
Rylai's Crystal Scepter
Quicksilver Sash
Aegis of the Legion
Banshee's Veil
Frozen Heart
Spirit Visage
Chalice of Harmony

The first 15 seconds of the game are the most busy for you.
First off, choose a good partner, this should be done in champion select to save time.
Quickly put a point in Hymn of valor and use it on the platform twice.
Grab a mana manipulator or meki pendant, depending on if your partner uses mana.
Use CV if you have it on there platform at around 8-12 seconds. Doing this, you'll have an idea of who you are going against and what they are starting out with.

Pictures, more in depth discussion on some things, and general completeness...