I don't have an ELO score(Level 29). But what I do have is tons of games with Karma. I got attached to her due to her amazing shield, her ability to both dish out a heal and deal quite some damage at the same time. You almost always win when the enemy team tries to tower dive you, due to your passive(which improves your AP the less health you have), and your ability to in a couple of seconds raise your health by more than 1k. Her speed buff makes her excel with melee champions, and she is able to solo lane - but should never do so due to her being a primary support champion.

Leave the carrying to your teammates, your tanking to your tank, and make sure to be there for everyone and people will love you.

Karmas biggest problem is her cooldown reliance and mana, and her AP needs to scale fast as the game prolongs our her abilities will be useless. But you should never have more than 30-40% CDR end game. And you shouldn't be scaling in HP/Armor/MR items, you may live, but it will leave you useless to your team. With a strong shield and constant healing and damage being dished out, you're at a good spot.

I used to build Karma with the Egypsian Lover build way, which I found most effective. But in higher level games, I've found a bigger advantage in making her your support with the kages picks and the philosophers stone for some mana regen. The philosophers stone later turns into a +25 tenacity, which is really valuable - with CC, Karma gets shut down easily - you can't shield or heal when your stunned, remember? Rabadons and Deathfire makes Karma a nightmare late game.

The skill you max out first is heavenly wave. Healing will come in handy. So don't waste your mantra charges. Learn when to mantra-wave and not, as a support staying out of battle with an AP-passive edge, you don't need to heal all the time, so save it for your ally or when you start getting too low. Mantra healing wave is much more important than Mantra + Shield. It makes you dish out more damage faster, making you have nuke potential, but when you're out of mantra and your teammates need you you would end up having nothing. Prioritize in healing.

Spirit bond takes time and practise. In the early stages it may end up coming to haunt you, draining your mana - and it will only be powerful in the mid and latter stages of the game, as it will be maxed out last. It only deals damage on contact with the ray, not on direct usage, so try to position your enemies between you and your ally, slowing and damaging them.

Heavenly wave requires you to be close to the enemy. Though spot huh? Not with your shield - it gives you the power to go in and out of combat unharmed, dishing out the heavenly wave damage you love.

Early game

Your job is to keep your bottom lane unharmed and harassing the enemy. Never last hit minions when your laning partner could have gotten the kill. They need the money more than you, instead focus on building gold per sec items for money. Place out wards. Try to avoid early agression until you have your shield. Don't use your spirit bond.

Mid game

You've turned out to become a potential jungler and agressive pusher, at level 8> there's a new safe source of income. Whenever your ally goes for a gank, roll in the dough, and when your lane and laning partner seems safe and your jungler is occupied, jungle for a bit. You can kill the blue buff at around level 6-8 alone, without smite. Your strength as a pusher lies in mantra + shield and heavenly wave without mantra, minions will just fall apart from it.

The reason for suddenly turning into a money-hungry player is that it helps you get rabadons deathcap and a steady source of mana from archangels staff quickly. You should never steal minions from your allies though.

Jungling

Here, rely on mantra + shield instead of mantra + heal. You want to jungle fast and efficient, and you won't as a healer.

Jungling for the blue buff holds potential, since the Karma loves the blue buff due to CDR, and early game for the mana. When you hold blue, your team has a sick support ally.

Late game

In the teamfights approaching at around the 20-ish minute mark, you'll be tempted to be close and dish out the damage. But this build is not for the agressive karma, but for the support. Stay behind your team at all times. Give them speed, give them shields, and give them heals. This build hence makes you dependant on having a good team, a reliable tank and strong carries who value you.