Your main role when playing as Kayle is to support your main DPS, making their carries useless and destroying the enemy team. Kayle is a really fun champion, for the low cost she is, Kayle definitly worth a try!

Pros:
- Can deal a lot of damage
- Good support, can heal, upgrade movement speed, and get someone invulnerable!
- Can be a pain in the *** to kill for the enemy team.
- Deals Magical AND physical damage.
- Awesome late game champion

Cons:

- Can't carry a team alone
- Can have trouble farming with her early game

My favourite summoners spells on kayle are ghost to escape your enemies, or to go after them to get a kill, and ignite, to get some kills early game, to get your Guinsoo's Rageblade as soon as possible.

Flash can also be a good spell, I used it a few times and it works great on kayle.

Teleport is another good possibility.

Exhaust is always a great choice for any DPS, although it has a shorter range then Righteous fury.

In my opinion, the best way to go with Kayle is 9xGreater Mark of Insight, since your main source of damage are Reckoning and Righteous Fury.
You could also go for attack damage reds .

As far as yellow goes, I like 9xGreater Seal of Clarity, providing you a great amount of mana regen early to late game, to be sure to have enough mana to use your ultimate, Intervention, frequently and to heal with Divine Blessing as much as possible.

For blues, I go with 9xGreater Glyph of Force, since they are good runes to go with your passive.
Greater Glyph of Celerity is another good choice for blues, more healing, more ulting= More support = More QQing in the other team :'(

For quints, I always go for 3xGreater Quintessence of Fortitude, it's the best way to go with Kayle.
CDR quints are also a good choice on Kayle.

Main build:
Early game: Start off with a Doran's Ring and a health potion, then go for a second Doran's Ring for more durability and mana regen/ability power. then get your boots of speed, and a Guinsoo's Rageblade, by starting off with the blasting wand. Then get your Sorcerer's Shoes, and go for the Nashor's Tooth. This is the base of your build. If the game continues, sell your Doran's Ring, and go for a Lich Bane, it's an awesome item for Kayle, be sure to start off with sheen. Then I like to go with a Banshee's veil for durability and to prevent from getting over CCed. Hexxtech Gunblade is a good choice to finish up the build.

Team with a lot of Magic damage:
Be sure to go with Banshee's veil, even before your Trinity Force. Force of Nature is always great against a team with a lot of mages.

Team with only Attack damage:
Thornmail! They'll kill themself if they only have DPS, by using your Diving Blessing Divine blessing and with thornmail's passive.

Other good boots:
Ionian Boots of Lucidity : More healing, More ulting, great choice.
Boots of Swiftness. Faster! Faster! Good choice on a Kayle, since she is a slow champion.

Against High hp:
Definitly go for Madred's Bloodrazor if you play against a champion like Chogath, Vladimir, or any other high hp champions. Madred is a great choice on Kayle, gets her attack damage really high, everyone will be affraid of you.

So, the final build should look like this:
|--- or ---|

Reckoning: Slows the enemy and deals a great amount of magic damage.
Divine Blessing Heals and boosts the speed of an ally or yourself. Don't be scared to spam this spell mid to late game, when your mana regeneration will be high.
Righteous Fury: Kayle becomes ranged, and throws fire out of her sword, dealing splashing magic damage. It's your best way to farm minions, be sure to have it on in every team fights!
Intervention: Gives invulnerability to an ally, or yourself. At level 3, it lasts 3 seconds, and makes Kayle really helpful to her team. Be sure to cast this spell on your carry when they get focused, or on yourself. Don't be afraid to spam this ability, it has a low cooldown!

Start off with Reckoning, if you want first blood and have a good teammate, it's the best way to go, since it deals a great amount of damage and slow the enemy. At level 3, you should have your 3 main skills , except if you are dominating and not receiving a lot of damage, you can skip upgrading Divine Blessing at level 3, and go for Reckoning instead.

Be sure to get your Intervention every time you can (lvl 6,11,16). It lasts longer and have a shorter cooldown every time you upgrade it.

Reckoning should be maxed first, then Righteous fury, and finish off with Divine Blessing.

To come...

To come...