OK, so I am a Platinum I support main at the moment (was Diamond 4 last season), and I've always had difficulties grinding elo as a support main. Only this season, I could sometimes have a hard time winning games even though I would be like 1 1 25 or something, simply because it is so hard to carry as support - and my skill on other lanes is not formidable, as my champion pool is low.
So Karma. My latest discovery. You cannot go wrong with her if you know what you're doing. If you don't - this guide is for you.

Pros:

-A lot of poking potential - can make a struggle for enemy bot lane early on, giving your adc an early lead in xp and cs if nothing else.
-Survives ganks easily - you've got slows, snare, movement speed buff to you AND your ally.
-Great damage source - although you yourself won't be dealing a whole lot damage to your enemies, giving your teammates a 4 man ardent censer buff can be quite big in fights. Also, you're quite relevant early to mid game.
-Sustain - Locket + E = Joy!
-Speed - you'll have over 500 movement speed without Cloud drakes.
-Utility - Late game, you'll have so much mana regen that you'll be able to pretty much spam your e just to move quicker.

Cons:
- if your team isn't at least even with your enemies, you're going to have a rough time unless you reach late. Karma is good on stomping oponnents and securing the lead. Making comebacks? Not so much.
- If enemy builds lifesteal early - you're f$%&ed

Can't figure out many cons at the moment. Karma works so well this meta that she doesn't have many flaws. Couldn't have said the same half a year ago.

OK, so the place you'll shine are teamfights. And the build above is designed for them.

Before the fight:

You've got some poking potential. Cooldown on ultimate isnt very long, so feel free to do R+Q if you think you can deal a chunk of damage to your enemies before the fight (be sure they dont regenerate health points so quickly).

Disengage

If the enemy team is engaging and you can't win the fight, use your talisman and R+E to escape. You will have more than enough movement speed to simply walk away (800+ on all teammates)

Now, if a teammate of yours is caught and doesn't have large chances of surviving, you don't let a homie down! Simply:

Engage

Which pretty much haves the same combo as engage lol. Simple really. First use talisman on your mates, then R+E (be sure to catch your caught mate!). Then snare the one who is either chasing your team the most, or the one you want to chase. However, don't do it if it's a stupid thing to do (Unless it would leave you in a 5v4 in a very late game. In that case, its probs lost unless you go in. Depends on situations ofc!)

So, your adc is at base, you need some gold. Make sure that you only get the minions he wouldnt get anyways, and that you dont influence the way the lane is push (unless you really need to push)

Most of the time you won't need flash in an agressive way - unless you want to kill someone who's low hp. Use it only to escape when you get caught.. Well you know what flash does.

Exhaust is most of the time standard. Do ignite if you really think you need it, it would normally depend on enemy comp.

R+W is not something you would normally do - only when you lack hp and think you'll need some of it later on. Make sure to not cancel it. Doing it when chased is a good option too.

R+E works great when taking drake/baron when you've got ardent (which should be your 3rd item). Try it.

Locket gives ardent censer buff too.

If you're the one getting caught before a fight, give your team all the shields possible. R+E has around 750 shield on lv 18, if not a little bit more, and considering you'll have more than 3000 health points in that phase - your team should be the one winning the fight if they play it right.

Don't really have anything else to add. Leave your comments below and I'll make sure to give you some feedback!
Enjoy carrying as support!