Janna Runes explained
There's one set of runes for Janna on patch 15.12 that is the clear favorite for LoL players and pros alike. The best Janna rune paths on the position 
Support are 
Sorcery as the primary path and 
Domination as the secondary path with a pick rate of 65%. Besides picking runes on Janna you should learn how to play Janna and if you are interested in pro matches take a look on how a pro builds Janna. If you want to discuss 
Janna then you should visit the champion subreddit.
Janna runes from primary path
Sorcery empoweres abilities of Janna and increases the available champion resources. Most of high elo players – and our LoL pros in the the major regions – have agreed that 
Summon Aery is the best keystone rune to run on Janna. This keystone rune adds more poke damage to your abilities. And additionally grants an extra shield, whenever Janna empowers or protects an ally with abilities. Other primary runes on Janna are 
Manaflow Band, 
Celerity and 
Scorch.
This is usually followed up by taking Manaflow Band for additional mana and mana regenaration. Celerity boosts all movement speed bonuses to Janna. Scorch increases your control in the early game.
Janna runes from secondary path
When it comes to your secondary path, most Janna players prefer to go with Domination. Domination improves burst damage and assassination tools on Janna. On the Domination path, the best runes for Janna are Relentless Hunter and Taste of Blood.
Relentless Hunter increases your movement speed out of combat due to every unique champion takedown. Taste of Blood heals Janna as soon as you damage an opposing champion.
FAQ for Janna Runes
Which is the best keystone rune on Janna?
The best keystone rune on Janna is Summon Aery. This Janna runes setup is then referred as Janna Summon Aery.
What runes does Janna use?
Runes from the paths Sorcery and Domination are the most used runes on Janna. For the exact pick rates of Janna runes used, you have to study the rune distribution presented.