Janna is a fantastic champion, and is by far the funniest and most CC strong support in the league.

I have put a fair amount of effort into this guide, so I do implore you to reconsider any downvotes pending the actual trial and testing of my guide that I imagine you are planning to do. And above all, thank you for taking the time to read this guide.

Pros
+She has lots of CC
+Movement speed passive
+Shield with high absorbation and AD buff
+High Mobility
+Hard to chase
+Good chaser

Cons
-Weak healing during lane phase

Mana regen: So you will be able to use your spells more often in teamfights and laning.
Gold per second: So you will have a decent income.
Cooldown reduction: So you will be able to use your CC's and shield more often in teamfights, it can really make the difference.
And Summoner's Insight for reduced cooldown on your Flash and increased affectiveness of your Clairvoyance.
And ofc increased XP so you wont get outleveled too much as you often will fall behind in XP as a support.

And then I go get some more cooldown reduction from the offense tree and 10% Spell Penetration for increased damage that often also can make the difference when going for kills during lane phase and teamfights late game.

Greater Quintessence of Health: With these, Janna is not as squishy, and therefore less likely to become First Blood.
Greater Glyph of Scaling Magic Resist: Is for teamfights and will often save your life.
Greater Seal of Scaling Mana Regeneration: Using your spells often may drain your mana quickly, these runes are ideal.
Greater Mark of Armor: Great for early game as carries have extreme high damage with their autohits in the first couple of levels.

What I recommend

This is your emergency spell/pickup spell when trying to land a CC for a kill.


This is just really good for spotting enemies at places you have not setup a ward when your team is feeling uncomfortable.

Optional

Also a good summoner spell, specially after the buff and also fits Janna good as she does not have that many heals.

This an excellent summoner spell if you are very trigger happy or your carry needs a lot of mana to spam his spells for example Ezreal.

As a support your role is obviously to support your team, exhaust is one of the strongest spells in the game and can easy turn around a team fight if you put it on the carry.

As a support I don't like saying which spells you should max, I always pick whatever that fits my carry the best, if he is taking hard damage from the other carry I would go straight for maxing Eye of the Storm so he won't have a too harsh time, if not then I'll will use the skill sequence linked above.

I do not like to say that THIS is the only good items and that THIS is the only order of buying your items. Keep in mind this built shows a standard way of buying your items, if the enemy team is full AD then I would make changes in my build to counter the enemy team. And if my team is getting pwn and early teamfights will happen then I recommend skipping Catalyst the Protector and rush an Aegis of the Legion to boost your team, always keep in mind that you do not have to buy your items in the same order but that you shall counter the enemy team and get the upper hand in that way. If you are low on cash because you lost bot lane and you are having a harsh time getting assists, turrets and dragons then I recommend getting a Heart of Gold after Boots to get some income.

Core Items

Philosopher's Stone
You would like to go back as soon as you hit 620g so you can start getting an income.

I simply do not upgrade these early game because Janna's movement speed is rediculously high.
catalyst the protector
This item will make your HP and mana keep flowing in laning phase or when helping out your teammates at other lanes.

This is a great boost for the entire team, rush this item if you have a very high flow of gold.

With these items you can keep up your HP and mana during lane phase and you have a high basic health to prevent people from killing you in one burst. This is OP stage, you cannot die now unless your opponents are really fed or you are trying to hug them.

Optional Items

I buy these boots for cooldown reduction, I have noticed that in team fights I often will just be ignored.

This is if you really do get all the CC's and their team has high magic damage.

Nice HP, mana and gives a good amount of AP for your spells.

Good item against AP team and to prevent CC's landing on you.

Great item, should be rushed if your team cannot catch up kills and people escape on low HP.

This is a very good item if the enemy team is stacking lots of magic resist but I would recommend having an AP fighter or AP carry to buy it instead of a support to get the full benefit of the item.

Just if you decide to go with the Heart of Gold I do not use Heart of Gold if I have a good flow of money which I have in most of my games.

This is a good item if your carry is having a harsh time getting mana at bot lane or if you have a mana burning midlaner for example Brand or Malzahar, it gives a very good mana regen and cooldown reduction for your team and also good HP buff for you.

What champion cannot use a Guardian Angel? This is a great item, high defensive stats and ress upon death, it is just great!

What Mage would not get happy when somebody at their team buys this sweet item?
Remember to always keep a good flow of wards in your inventory, I normal carry 5 wards all the time.

This Picture shows which places that should be warded as a standard.



This picture shows places that should be warded under these circumstances.
This is for defensive warding, if the enemy team is pushing you a lot and all your outer turrets are down, this is great for preventing them from ganking you or ganking them when they try to steal your buffs.
These wards should ALWAYS be placed so you easy can counter your enemies trying to do dragon / Baron.
This is if you are pushing your enemy team a lot and you want to be safe when running around in their jungle, crossing lanes trying to push them.
This is for ganking the enemy team jungler and gank the enemy team when they pickup buffs early/midgame.

A little trick for you: If your jungler is having a hard time ganking your lane because of wards then either buy an oracle to clean out the wards or buy a Vision Ward so you can take out the enemy team's wards and then your jungler can gank again, see wards as a gold per sec item and not as a DOH it burns up all my gold item.

She is a champion that has high CC and movement so she easily can catch up escaping enemies. With this build you will be a little bit tanky so you can be offensive and place your Monsoon to make the perfect knockback for your team. Wards are gold per sec items, not a "DOH it burns up all my gold item". I cannot come in mind of something worse than a support that does not place wards.

This is the support I play when I go premade with my friends so far I have only experienced good games with her and she is really good both in low and high elo games.

Please help me improve this guide, if there is anything that I did not mention or if I have wrong spelling somewhere in the texts or something does not make sence, then post it and I will fix it to make a better guide just for you!
Thanks :)