Hello. First let me say that this is my first guide, so if there is something that needs clarifying, please let me know in a constructive way. Second, I'm not saying this is the only way to play Karma, just one that I have found to be HIGHLY effective, assuming your team cooperates with you and doesn't feed. The main focus of this build is that it hits 40% CDR relatively early, and maximizes on shield damage/shield. Your job in the game is to push lanes while the enemy is distracted, and to keep your allies alive while throwing down some decent magic damage. Your team is your friend. Don't be afraid to put your shield on your allies. Especially those that tend to get focus fired. Lastly, your heal is very good when team mates are below 50% hp, which makes her a good counter to people like Karthus or Ezreal ults.

I use Magic Pen marks, because your main damage output is magic damage. This will make your skills hurt a little more.

I use flat mana/5 Seals to help with the early game mana problems. After you get Tear of the Goddess and Philosopher's Stone, you shouldn't have to much mana trouble. This is doubly so after completing Morello's and Archangels.

AP/level Glyphs are to help out some in the end game by increasing your shield strength, and 28 AP is another 1/2% restored on your heal, which helps.

I use Gold/10 Quintessences because her items tend to be expensive, especially early game. This helps more than a lot of people realize. It's not a TON of gold, but it allows you to back earlier to buy important items, and the time advantage is what we're going for here. Also, this will allow you to share the last hitting with your lane partner instead of being a greedy *****.

I use a fairly standard 9/0/21 here, with special note to only put 1 rank in Intelligence. Anything else is wasted, and I'll explain this later with the items. Feel free to adjust Summoner Spell upgrades as you desire (TP or Ghost upgrades over Flash or Clairvoyance). I wouldn't suggest taking Clarity, simply because after around level 7 or 8 she doesn't have mana problems with the items listed here. You'll wind up wandering around with full mana all the time, and have no use for it, aside from being a good teammate and helping your mana starved allies.

The purpose of your items are to get you to 40% Cooldown Reduction (CDR) quickly, without wasting effort in surpassing the 40% cap. After that you simply maximize your AP to boost your shield and your heal, as well as your damage output. All of Karma's skills scale well with AP (.6 to .8 gain). I start with a Meki pendant and potions to help with early game mana problems. You can start with a Doran's Ring if you'd like, but I prefer the meki pendant cause I can quickly build it into Tear of the Goddess(TotG). I wait until I have 1400 gold in lane and then base (assuming the lane is covered) and buy Philosopher's stone and TotG. These almost completely alleviate all mana troubles, as well as provide some HP/5 and most importantly, gold/10.

After the mana troubles are covered, it's time to focus on hitting 40% CDR. Note that there is a hard cap that you can't exceed 40% so anything above that is wasted effort. I start with 5% from masteries, and go for Ionian Boots for another 15%. This puts me at 20% CDR, and in need of another 20%. The release of Morello's Evil Tome has solved this issue perfectly by providing even more mana/5, some good AP, and the last 20%. These two items are the reason you should only put one point into the Intelligence mastery. we get a nice 40% = 5% + 15% + 20%.

Now that we have cooldowns maxed, you should be focused on maximizing your AP. I like to finish Archangels before building Rabadon's deathcap but the order is really up to you. Now that your AP is ~500, it's time to consider some survivability. With your high damage, I like to go spell vamp with Will of the Ancients, though you could just as easliy go for a Ryalia's Crystal Scepter, or Abyssal Scepter. At this point it's usually a little late in the game to go for Rod of Ages so if you really want to use that I'd suggest doing it after boots.

This puts you at 5 items plus a Philosopher's stone. If you haven't won the game yet, feel free to sell the Philosopher's stone and buy the defensive item of your choice. Guardian Angel isn't a bad choice because you can shield yourself upon re-spawning as well as heal yourself considerably.

In the end you should have the following items:
Archangels Staff
Ionian Boots of Lucidity
Morello's Evil Tome
Rabadon's Deathcap
Defensive AP item (Will of the Ancients, Rod of Ages, Ryalia's Crystal Scepter, Abyssal Scepter)
Defensive item (Guardian Angel, Thornmail, Force of Nature, as appropriate for enemy team)

Q: Heavenly Wave
This is Karma's second bes skill. It's a nice damage cone. However, if you spend a mantra charge on it, it also becomes a heal. This is AMAZING in team fights or right after a team fight. Because it's heal is based on % of missing HP, it is a tank's best friend (Cho LOVES this.) The healing scales at roughly 1%/50AP healing, so by end game you will heal at around 20% of missing health. DO NOT UNDER ESTIMATE THIS. On a high HP tank, this will heal for upwards of 1k HP if they are low. With max CDR you can fire this puppy off every 3.6 seconds. So don't be afraid to use it right after your shield. It'll be back up as a heal quickly if you need it. This is secondary to Soul Shield, but should still take priority over Spirit Bond

W: Spirit Bond
Spirit Bond is very situational, and my main use for it is to get back to lane faster, or to help an ally get into position for a gank. While it does deal damage if you move the bond through an enemy, it's much harder to do than any of her other skills and requires either a team mate to help, or some lucky minion placement. Note: You can NOT leash to invisible units or wards as the leash will immediately break. Mantra only doubles the move speed bonus, which while nice, is not as powerful as her other skills. Put one rank in it at level 4, and then wait till you have to to rank it up.

E: Soul Shield
Karma has THE most amazing shield in the game. It can be placed on an ally at decent range, and if you spend a mantra point, it deals lots of damage in an AOE that is the width of the lane. By this, I mean that if you stand in the middle of your lane, and cast the empowered shield on yourself, you just hit the side walls with the damage AOE. THIS IS HUGE. Put ranks in this skill at EVERY opportunity. The shield damage is equal to the shield strength, and it has the best AP scaling of her abilities.

R: Mantra
You start the game with this skill and it can store up to two charges. Early game, use the charges with your shield to harass enemies almost for free, or to help heal your team mate up if they were in a tight space. The base cooldown is 30 seconds, which reduces to 25 seconds at level 7, and reduces further to 20 seconds at level l3. With max CDR, this gives you a new Mantra charge every 12 seconds at level 13+. This is what you want. It means that you can begin a team fight with two stored charges, initiate with a damaging shield, hold out for either a heal or another shield as necessary, and have another charge to finish up the fight/chase with at the end.

I use Flash and Clairvoyance, though these are subject to your play style.

Flash: This is a great escape skill, and coupled with your leash can also be used offensively. Spirit Bond to one of your own creeps, and then flash to the other side of the enemy to catch them in the bond. Also it is a good entry mechanism that allows you to tower dive very effectively to clean up kills under enemy towers. By flashing in and casting a mantra-Soul Shield - Heavenly Wave, you can burst weaker characters to death quickly, and then walk out from under the tower while your shield tanks for you. Highly Recommended

Clairvoyance: This one is a little more personal preference, I like it for the team intel it gives. It's good for finding enemy junglers, or scouting ganks early. With this mastery build, it's up after 42 seconds, and lasts for 10 which is impressive for a summoner skill. Finally, it can be used to deter enemy movement because they will know you can see in that area and will be forced to move.

Clairvoyance could easily be switched out for Teleport, Ghost, or Exhaust as you see fit or fits your play style. If you wanted you could take ignite instead but I'd keep the mastery point in 15% magic pen.

Clarity: DO NOT TAKE THIS. It will be useful once just before you base for the first time, and useless to you afterwards. Your items will cover all mana problems.

Karma is very good at pushing towers because her shield is very strong and has a relatively low cooldown (6 seconds with full CDR). Late game the shield will block over 700 damage, which is a good 3 hits from a tower. By placing your shield on minions when attacking a tower, you can maintain your minions there for longer which will result in more damage. Be careful while doing this because it means your shield isn't available for yourself.

If playing against a Karthus or Ezreal, it's often a good idea to keep a mantra charge in reserve, to provide last second healing to yourself or your lane partner to prevent death by global ult. It also works vs thinks like Ashe's arrow. I can't tell you how many times I've saved a team mates life using either a shield or a heal at the last second.

Karma is an excellent farmer after reaching around level 7 or 8. her mantra-Soul Shield-Heavenly Wave combo will kill entire waves of minions. After completing Archangels, you only need a mantra-Soul Shield.

While everything I've said about damage output is true, and she does hurt like a truck, Karma is first and foremost a support hero. Your job is to look after your team mates first, and deal damage second. Your heal is a HP tank's best friend, and your shield will give your carry time to get those last few shots off.

Spirit bond to allies while running away to help save them from bad situations.

Karma can do a lot on her own, but she really shines with the backing of a good team behind her.

yes, I've done this. It's awesome. First in items, swap out Will of the Ancients for a Hextech Gunblade, and sell your philosopher's stone for a Lich Bane. Also get Red Buff and the 3 buff potions. From there it's all about keeping your shield up and staying mobile. User your mantras as you can but save one at the start of battle. Start combat with a Mantra'd shield to give a little burst damage on him, auto attack twice, then use Heavenly Wave. Keep alternating your abilities with two auto attacks in between. This is to use the lich bane charges, as well as give Lich bane enough time to cool down. As for your mantra, if you're above half health, use it on your shield for damage. If you're below half, use it on heavenly wave to heal up. All in all, this should take you maybe 15-20 seconds, 30 seconds tops. Also remember to keep moving around him to dodge some of his attacks.

Updates to come: Adding pictures to discussions of items, runes, and skills