Hi, I'm Kaytree, and I'm a diamond support main. Enjoy my guide!

Janna is one of the easiest supports supports to play. Her playstyle is incredibly low-risk, but high reward. Her teamfighting, chasing, kiting, and disengaging abilities are all pretty strong. Janna is a shielding, peeling machine that can be picked with pretty much any team comp. With Janna, you can keep your teammates alive for a long time, and protect carries easily. You can also interrupt a lot of damaging spells and gapclosers with your Q, such as Leblanc's Distortion, Irelia's Bladesurge, Leona's Zenith Blade, Nidalee's Pounce, etc.

Janna is best when:
-the enemy team has hard engage
-the enemy team has wombo combo based teamfighting (wukong, kennen, etc)
-your team needs peel
-your team has a hypercarry

Pros
+Very strong disengage and peel
+Decent laning phase
+Good mid-lategame
+Insane mobility
+Good catch potential
+Really strong survivability

Cons
-Weak against poke in lane
-Squishy
-High mana costs

Exhaust: Usually best on Janna, especially if the enemy team has assassin or burst champions such as Zed and LeBlanc. Plus, it's another handy spell to add to your arsenal of peeling tools!

Ignite: You can take ignite if you want more kill pressure in lane. Janna does not have much kill pressure in her kit, but if you are laning with someone like Graves, ignite can be good to add to the burst/kill potential.

Flash: You always want to have flash on Janna. You can make flash-ult plays, or escape from dangerous situations.

Starting items
For Janna, it is best to start Spellthief's Edge instead of Ancient Coin. Spellthiefs edge gives you combat stats, whereas ancient coin does not. Combat stats are always better for laning! Buy 4 Total Biscuit of Rejuvenation if you are against a POKE HEAVY lane, such as Nami, Karma, and Lulu. Otherwise, it is usually best to buy 3 Total Biscuit of Rejuvenation and 1 Mana Potion.

Core items
Try to get Sightstone on your first back, and a Vision Ward. You do not need to rush boots on Janna, because she already has high movement speed without boots.

Mikael's Blessing is always a good item on Janna, unless the enemy team doesn't have any cleanse-able cc. This item gives you CDR and mana regen, which are amazing stats to have on Janna. It also gives your carries a significant amount of health, as well as a cc-cleanse, which can mean the difference between life and death. Remember, as Janna, your job is to PEEL and do everything you can to keep your carries alive. I usually rush mikael's after sightstone, because it's just such a great item on Janna.

Locket of the Iron Solari is also a good item on Janna, because who doesn't like more shields and peel? Get locket if the enemy team has magical threats, or bursty/aoe teamfight threats like Hecarim and Miss Fortune.

Mobility Boots are nice to have on Janna, as well as any other support, because you can roam around the map quickly and get vision control.

Get Oracle's Lens when you can. It is a cheap upgrade that gives you a lot more vision control.

Vision Wards are important to buy and have on the map! Many people underestimate the power of pink wards, but they can give you a lot more control, safety, and pick potential. Try to always have a pink ward in your inventory if the enemy has invisible champions, such as Rengar, Vayne, etc.

Upgrading your support item
I usually don't upgrade my support item until I have all my core items completed, because the core items mentioned above are a lot more useful to have in most situations.

You can choose to upgrade to Frostfang early on if you want, for increased gold income. However, do not upgrade to frostfang if you plan to purchase talisman of ascension later on in the game.

talisman of ascension: Buy this item if you need disengage or engage. If the enemy has engage using Turbo Chemtank, such as Gragas, Maokai, etc, then you can get talisman to counter that. Talisman is also a lot better than Frost Queen's Claim in the late game.You can still buy Frost Queen's Claim on Janna if you want more ap, but I don't think it is that necessary on Janna.

Situational items
Zeke's herald is a good item to get if you have a lot of AD threats on your team, or if your adc needs more lifesteal.

You can purchase ability power items, such as Morellonomicon, Rabadon's Deathcap, etc. if you are ahead. I'm not really a fan of these items, but they are viable. Mejai's Soulstealer is a decent item on Janna, because you can get assists easily and you don't die a lot.

Twin Shadows can be a good item to get for more vision control and pressure. It is especially good against champions like Evelynn, Twitch, and other invisible champions, because you can scout them out with the active.

Buy Randuin's Omen or Frozen Heart if you find yourself dying or getting chunked a lot by the enemy's ad threats. Randuin's is usually better if the enemy team has a lot of mixed damage or armor pen, because the health will benefit you a lot more than just flat armor. Get frozen heart instead of randuin's if the enemy team is full AD, or does not have a lot of armor pen.

Always start E if the game is proceeding normally. If you are invading or getting invaded on, start Q.

Get Q level 2.

At level 3, you can put another point in E if the enemy botlane has heavy poke or burst. Otherwise, just level up W.

Max R>E>W>Q.

Early Game
Help your adc push at level 1 by autoattacking the minions. If you get level 2 first, you can go aggressive with Howling Gale. Try to sneak in autoattacks and W's on the enemies, but avoid hard and extended trades. Don't forget that you are extremely squishy! Going overaggressive and getting caught by a Dark Binding could mean your death. Don't worry if you find yourself losing lane. Janna is not the strongest laner, but she excels in the mid and late game.

You can try to pull off roams to the mid lane if your adc does not need you or is not in lane, but keep in mind that Janna's ganks are not that strong.

Mid Game
During mid game, you want to ward and establish vision control with Vision Wards and Sightstone. Ask your teammates to help you get deep wards, and try to control the dragon area with pinks and sweepers. Group up with your teammates so that nobody gets caught. If you are standing with your teammates, they should always be safe.

Late Game and Teamfighting
Late game is when Janna shines. At this point your Howling Gale will be on about about a 10 second cooldown or less, so you'll be able to spam it and interrupt enemy engages and gap closers. In teamfights, stick by your carries and spam your shields. Use ult and Q to prevent enemies from jumping on your carries. Don't forget to use your item actives!

When and where to ward
Warding is very easy and quick on Janna, due to her high movespeed. Make sure to always be warding!

During the early stages of the game, try to find out if the enemy jungler started bottomside or not. If you see the enemy botlane go to lane a few seconds later, or if they are missing some mana, you know that they leashed the enemy jungler on the botside jungle. Take this into consideration, and ward the river early to avoid getting level 2 ganked.

A general rule of thumb is, if you are pushed up in lane and don't have vision of the enemy jungler, go ward the river. However, do not leave your ADC in a dangerous situation. Tell your ADC to play back for a few seconds while you go ward.

If the enemy has a jungler that can solo dragon early on, such as Nunu & Willump or Udyr, then coordinate with your team to always have vision of the dragon or the enemy jungler.

*Quick tip - During laning phase, if you back without enough gold to buy Sightstone, always buy one or two Stealth Wards and a Vision Ward if you haven't already.

Try to always have 1 ward in the tribrush, 1 ward in the river brush across from the tribrush, and 1 ward in the lane bush behind your enemies. When your adc does not need you in lane, try to roam around mid and place wards around the dragon area and the mid lane to give your mid laner some protection.

During mid and late game, your job as a warder is just as important as early game! Try to place deep wards, and use Sweeping Lens and Vision Wards to catch out enemies with your team.

Here is a map of some generally effective warding locations.

Thanks for reading my Janna guide, hope you learned something from it. Feel free to leave questions, comments, or suggestions.