Why Karma you say? well shes a high hp mage/support

Pro's:

High hp
very well 1v1
very good ganking partner
aoe heal
can do up to 1k dmg aoe with her opening combo
super strong solo lane
fairly easy minion farming and harass skills
basically a jack of all trades (except carry)
AP scales well

Con's

no huge ult compared to other champs
master of none (she cant nuke like veiger, cc like amumu, or tank like rammus)
very situational timing for abilities
must get up close in a fight (which mages dont like)

Runes are fairly standard for a support

Red -Magic pen
Blue - CD reduce
Yellow - Mana regen per level
Purple - Flat hp

Core items:
Ionian Boots of Lucidity
Rod of Ages
Banshee's veil

Why: Karma requires a little bit of everything early on and these are the most cost effective items for that. plus gets you involved in 5v5 fights without a worry

Recommended items:

Spirit visage - Recommended (not needed)
* 10% cdr and 15% healing kind of a preference but you can decide to get
Rabadon's Deathcap before hand

Rabadon's Deathcap - Recommended (Late game only)
* Synergizes with Karma's passive and gives a large amount of AP

Zhonya's hourglass - Recommended (preference)
* Team has a strong AD champ picking on you? Get it

Abyssal Scepter - Recommended (preference)
* Team has a strong AP champ picking on you? Get it

Will of the Ancients - 50/50
* This is a team based item since it gives you team 20% spell vamp.
so if 4/5 teamates (including self) is AP focus then yes but after
Rabadon's Deathcap

Rylai's Crystal Scepter - Not Recommended
* all your spells are aoe thus 15% move speed debuff is bad

Morello's Evil Tome - Not Recommended
* With runes, boots and a kindle gem you have you mantra spell at 15-18 seconds
already no reason to get past that

Frozen Heart - Not Recommended
* ONLY get it only if your tank doesn't and you have all your items you want

Mejia's Soulstealer - Not Recommended
* If you are 10/0/5 in the first 20 mins and your team score double you
opponents then get it

Heavenly Wave:

Bread and Butter move (most important)
good damage output
% based healing output
most used move for karma
Strong harass
the spell is bigger than it shows
AP scales well

when to use it:

5v5 team fights - use it to heal as many allies as possible and hit as many enemies too
Lanes - Harass and heal self and allies
Ganks - even vs 1 person it takes a large chunk of hp


Spirit Bond:

Makes or Breaks Karma
Karma's most effective ganking tool
Karma's most effective retreating tool

When to use:

Save an ally when its 2v5
mantra + enemy = runaway solo or gank team
if you can reach an enemy in a gank speed up the ally nearest to the person you are ganking
5v5 team fight hit someone near the back of the enemies like the range carry and make the
beam hit people


Soul Shield:

Good aoe dmg
Good shield
Scales well
can turn fights
Dumb damage range (super far)

When to use:

5v5 team fights as soon as tank has 3-5 people near him or her mantra shield
save carries and allies who are having trouble and are about to die
ganking if they run and you have a melee champ near the enemy with 1 hit left can do a kill
at about the range of 4 times her basic attack


Mantra:

Amplifies abilities

When to use:

When you want Heavenly Wave to heal
When you want Spirit Bond to amplify move speed
When you want Soul Shield to do damage

When playing Karma and you see a minion wave run into the middle of the wave and cast mantra soul shield and follow up with hitting the creeps with a heavenly wave after about level 10 should clear them pretty fast