Hello,

Let me introduce you Janna, she's a very strong support if use properly. And by that i mean if you can shield your adc properly.

If you do it too soon the ennemies wont attack, so you wasted mana.
If you do it too late, well it's too late and all the damages are already done.

That's the main aspect or her early gameplay.

This aspect is crucial too. Janna's shield absorb damage (ofc it's a shield) but it gives AD aswell. You should use it at your advantage by shielding your ADC when he wants to trade auto attacks with the ennemy ADC. Most of the time the result is the ennemy ADC lose HP and your ADC is still full life.

I highly recommend you to play janna with a premade ADC, its easier to be synchronized with someone you can talk to.

the Q:

This spell is so strong in teamfights, but the only way of making a good use of it is by training a lot in order to know the range, the speed, etc.

It's a really good engage/disengage spell too.

The W:

Don't bother using it to harass and always try to have it when your jungler is ganking.

Important : Never use her ultimate in order to heal. If you don't play AP janna, the healing is really low and doesn't worth wasting a good AoE CC with a high cooldown.

There's 3 ways of using janna's ult in my opinion :

1: Pushing ennemies under your tower, by flashing or walking behind them and then ult'ing.
2: Pushing ennemies whom are trying to escape into your allies.
3: Pushing ennemies away from a dying allie.

Janna is one of the most powerful support in the game, but she requires you to train a lot with her. You wont always make perfect ultimate or shield with a perfect timing, so don't blame yourself if you fail, just train and improve !!