Hello my name is Kirlin and this is my first guide. I will try my best to improve it as I am still learning how to. I am a Diamond support main in the EUW server.
This is my OP.GG: https://euw.op.gg/summoner/userName=kirlin.
Hope you find this guide helpful. Any feedback will be appreciated.

Pros:
Has great poke and lane dominance.
Has good base damage.
Has good lane matchups and can win everyone if played properly.
Has huge shields to peel and speed your whole team up.
Cons:
Damage falls off mid to late game.
Has no escapes other than a speed up on E.
Prone to die if she engages wrongly.
Empowering the wrong ability with R can cost your team a fight.

Poke poke and poke. It is a must on Karma. She is the best poking support early game since she has R lvl 1 to empower his abilities. Abuse her lane phase because at lvl 6 you will not get a significant powerspike like enemy support. AA (1 sec) and abilities (2 secs) landing on enemies reduces R CD. When all-ining use Ingnite ASAP to reduce enemy heals by 50%.
Control the tempo of the botlane (control when pushing and when not) to be first to sneak into river to help in early skirmishes (junglers/mid laners) and create pressure since enemies do not know where you are.
AFTER FIRST BACK: Control ward the river bush after your first back if your jungler/mid will not do it. Ward enemy raptor bush (or Raptors if enemy jungler is MIA) to know when he goes for his second red buff. Sometimes you would be able to go and RQ steal it.
Be sure your ADC can safely farm his lane (vs Leona/Alistar dont roam that much) and get to lane before the enemy minions hit your turret. Your mision is not to only to support your ADC but to control the vision and try track the jungler (always look at the minimap once per 10 secs). Your damage is very significant yet and you can be thought as a second AP damage threat similar to a mid laner.

Control the vision WITH AT LEAST one member of your team. If you go alone and get caught you may as well lose the objetive you had been warding for.
If your goal is Drake/Nash, ward that side of the map as deep as you can safely do it. Use your E to move faster and get to places before. RQ is less valuable now and RE is better option. Remember it applies Ardent Censer passive to all your team.
Before backing if you have not used all charges of your Sightstone, do it. It will refill at base anyways and enemy team will have to put Sweeping Lens on CD to clear it.
Control wards are key in this moment of the game since you can engage very good into 1 or 2 enemies with E->RW (to not get blown up)->Q.

Same vision goals as mid game.
Here your RQ is pretty much for a 100% win pick on enemy team since it slows. RE is your bread and butter now. Spam it as much as you can. Stay on the back of the teamfight and peel your carries. Your shields provide speed too to run away from enemy divers and AOE damage.
TIP: R starts CD when you press it and you have extra 8 seconds to choose your ability.
TIP: Redemption can be used after death so do not rush using it before dying.