My name is Anthony, and I am support main and have been for the past year. This is my first guide so don't be too harsh :) I main Janna as she is my favourite support with Leona following up.

I choose the runes and masteries so that at level 18 Intelligence and Glyph of Scaling Cooldown Reduction Will give you 10% CDR allowing you to use abilities more often.

Expose Weakness Allows your allies to deal increased damage to enemies when you hit them with your abilities, usually your Howling Gale.

With your Eye of the Storm Ability, at the start of the game upon casting it on your ADC will grant them 1.5 AD which will help them CS a bit easier and do a little bit more damage in trades.

Janna Is a very strong team fighter due to her utility and peel. in a team fight you should be about in the middle of your team and when your allies start taking damage you will want to use Locket of the Iron Solari to give them a big shield to allow them to survive longer in battle. When your team is diving a turret or is starting to get to about half health, using Redemption can heal your allies for a good chunk of health and can damage any enemies in the vicinity. Try to poke enemies and stack your Athene's Unholy Grail so that you can heal any low allies with your shield.

Janna's Howling Gale is very useful in team fights because when fully charged it will reach there backline and CC all enemies hit for a few seconds leaving them venerable. Her ultimate , Monsoon Can push enemies trying to get into your backline away and heal your allies in the vicinity while doing so.