i have two boots up there because the Ninja boots are better if the other team has a lot of Melee champs. if they don't, then Lucidity boots are find.
you'll also want to sell your ring to get more armor or AP. while it is important to get Sight wards, i generally don't get them until i return back to base (or die) and stay and support. if the other team has a Jungler, go back once you get a kill or two and get them to save from ganks. you need a lot of items to be a good support/tank/ap build, but you are a support and need to get wards so adc can ...carry.
if your not needed so much as a tank Worry more about the AP than the HP/defense.
If your foes take a large amount of Magic resist, get Abysseal if you see fit, but always Banshee's Veil is nice to have.
when played right, i have gotten 5 assists in early game with a good Adc around me.



Even with Karma as the tank, it's best NOT to run in unless your whole team is around you. You'll probably have the most HP, but her defense isn't always the best. so make sure you're using your shield accordingly. While Karma can heal, it's never a good idea to rely on her to do any significant amount of it. So save your R for her Link or shield to do some damage or catch up/slow and enemy.
Also remember, while karma is AP for the most part, she is still support or tank. Killing a wounded foe won't pose difficult, even if at full, but when ganked she can become useless, so always remember your surroundings. Seems all pretty basic i know.
Karma can farm minions very well. if you see a large group of them, run into the middle use your R and then your E. this should kill or almost kill all of them. if it doesn't use your Q, (after positioning yourself to slay them all) on what remains.

Karma as a support should Focus her shield more, and W at 1 is good around lvl 4,
her Q heals with her R active, so it's nice to start with, to damage and heal teammates.