Janna is fun because she has really three ways she can go: support, dps, or mage. There are better mages, better dps's, and better supports, but none that are as great at all three. This is what I capitalize on in this build. Another thing that is amazing about Janna is when she does go into one of those builds (a mage, say) and she beats someone like veigar 1v1, it is lolz :D

Noobatize: "To noobatize": defined as "to render someone a noob."
This is a very important term in playing Janna. She is unpredictable, and thus quite often renders her opponents noobs.

I have tried a number of builds with Janna and found this one is the one that works every time. DPS Janna can be really fun, and so can AP Janna, but she is really most useful with a bit of everything.

Getting some health, max cooldown reduction, some AP and damage is nice. Rageblade may seem unlikely, but you will be attacking more than most mages. With your shield giving you bonus damage, attack speak increase makes a very big difference. You whirlwind, throw your bird, and smack them up with your activated shield. If they start winning, ult and run, or ult and heal then chase.

This build was inspired by a fantastic video I found on Youtube.
http://www.youtube.com/watch?v=FrsTE1vpoXM
I did not make this video, and it is outdated as Janna has since then been nerfed, but it is still awesome.
Since her shield is now nerfed, you need more cooldown reduction than the video takes into consideration. Increasing AP is good, but for your shield only increases the protection and not the damage, so keeping it up more often is better than keeping it stronger.

Hope you all enjoy, because Janna is epic and not many people play her, and of those that do most suck.

Still haven't experimented much with these, so any suggestions are welcome. I like to be fairly offensive, so this is what I use.

Cooldown reduction is essential for Janna to be any use to herself and her team. That being said, the sooner you get the Tear and the Soulstealer the better you will do. The Soulstealer is great for Janna because she seldom dies and often gets assists. I like to get the Kindlegem before the Soulstealer, though, because it gives her some much needed early health and cooldown reduction.

I have never played a game where I finished my item build, because by then I've already won, but maybe if you do, you could substitute an item for a Deathcap.

This will somewhat depend on how your team is set up. If I am soloing a lane (either middle or when there is a jungler) I like to get my shield on par with my cyclone so I can survive better.

If I am laning with a tank or a mage, I will max my cyclone before my shield, so I can get some bigger damage out there, or if they underestimate the range then some nice early kills.

If I am laning with a dps, like Pantheon, then I like to max my shield first and rock the house.

Clarity is without a question.

The teleport can nicely be replaced with ghost, cleanse, or flash. Ghost is nice because Janna is the master or escapes and chases. Cleanse is good because the only way you will ever die is by being cocky or by getting CC used on you. Flash can be used early game if they get too close to your tower to flash on the other side and ult them into the tower. This isn't easy though. And teleport is handy because you want as many assists as possible, and you can earn lots of money pushing creeps. Janna is a pro laner.

Always hit the whole creep wave with your cyclone. Spam it, because you have clarity and you want to go back for your tear as soon as you have $600 anyways.

Most of the time hitting the creeps lets you hit enemies too. If they get smart, you can usually angle it to the left or right so they dodge into it. This does nice damage early game.

She can tower dive nicely with her shield, but be careful.

Early game you will be maintaining a steady push, quickly wittling your enemies and their tower. Keep your distance, and every time they make a mistake administer a little pain. A few free hits here and there really adds up early game. At level four, you can tower dive fairly well and they won't expect it. They will be at low life, carelessly not going back, you will be at full life because nobody can harm Janna, they will hug the tower, you shield, run up (not drawing aggro), cyclone bird smack smack done. While they are gone, you kill their tower and then go gank.

While pressing towers (which you will do a lot), stay just out of range. If the enemy comes close enough, hit them, if not, hit the tower. At this point you can use your cyclone to zone control: charge it up like a wall, and they dodge left you stay right and smack the tower.

Your early game goal is to rack up assists (or even kills), and ascend as soon as possible to full blown pimpery.

Her ult is multi-purpose. It can be used defensively, it can be used out of battle for a heal, it can be used to split up teams, and it can be used to push enemies into towers or allies. It can also be used to interrupt other people (like Nunu's ult).

The skills you need to develop as Janna are timely shields, and well aimed/quick reflexes with the cyclone. Hit people behind you as you run, hit people running from you, hit people ganking you from the sides, shield allies when a tower is about to hit them (this is useful for when they are about to die as well as early game just keeping them healthy). Also you can block people's nukes, and depending how fed Karthas is you can sometimes block his ult on yourself or allies. This is what makes Janna so much fun, blocking hits just in time and getting away with virtually no life :D

Pros:
-She is very often underestimated. People at low life will always over-extend to kill you if you are low too, forgetting you have a shield.
-The range on her cyclone is often underestimated too.
-She can easily escape ganks in most cases.
-She is very good in team fights (spam shield and cyclone, and hunt people down with your bird).
-Great laner. You can usually kill towers sooner than anyone else. Also great in a 2v1 lane, because they can't push the creeps without taking damage from your cyclone, and you can stay at a safe distance.

Cons:
-She does not have much burst damage.
-She is susceptible to CC (especially with this build).
-Team fights will often target you first, because you are annoying and squishy.
-If Nunu is on your team, your ultimate will **** block his.

1. Whenever you are fighting someone 1v1, sing "Can't Touch This."
For reference: http://www.youtube.com/watch?v=otCpCn0l4Wo

2. Whenever there is an attempted gank on you, as you retreat sing "Break My Stride."
For reference: http://www.youtube.com/watch?v=cy46iOwWQiE&feature=fvw

3. At the beginning, just stay by your tower and shoot cyclones into the grass. Or, if your ally goes into the grass, then stand in there and shoot cyclones at their tower/heroes.

4. When covering someone's retreat: use your bird to slow the immediate pursuer, shield your ally, cyclone the pursuer. Use ult if necessary, but beware of launching the enemy further towards your ally.
*Caution: this can lead to you dying instead of your ally. Or, worse, your idiot ally turns around thinking you are making a counter strike.
*Caution: if you are the one escaping, don't use your bird on them unless you are sure there is onyl one, as you will be slowed as well.