Karma is a good lane bully. R+Q or just Q. Try to harass enemies as more as you can. But don't loose your head - remember to find middle between poking and mana reserves.
Karma is FAST. This champion is concentrated on movement speed and cooldown. Play with these two in TF.
One of the best champion for escapes. You can buy a lot of time for your team to run away just from R+E -> W(fastest enemy champion) -> Q.

Mana hungry. Never loose your head. Always leave mana for 2 abilities.

I recommend first 20 minutes to play your ulti with Q. later in TF use your Mantra more with E. With R+E you give HUGE advantage for your whole team.
Also, i recommend to bite yourself. Clear bushes from wards, then tell your team to wait you in bushes. Then show yourself for enemies. When they attack you, run straight to bushes, where is your team. Don't forget to R+E -> W -> Q. Also press queens blade active. It will slow enemies down. Quickly escape from fight (mabye flash) and watch how your team strikes. I don't say to run away, just stand somewhere else, and grant buffs for your team.

This is my first guide. I play as karma for about 80 games now. By the way sorry for my English, it's my third language.

ALWAYS REMEMBER. you are support. You don't do damage. You ward, you predict where enemies can be and you stun, slow, shield, heal.

When TF start's don't play with Karma i first row. You have to run around your team fast and grant them buffs. With more experience gained, i will add more in this guide.