Janna will try to poke as often as she can with her W and auto-attacks. If you’re playing as a melee champion, try to minimize your time spent overextended while getting warding quest stacks.
She may wait for her Shied E to be up before trading. This pattern is pretty common against champions who can return fire when she looks to trade. Use the E cooldown time frame to poke her.
When playing as a melee champion, make sure Janna doesn’t bully you down with basic attacks. When you can’t engage, stand out of range and in line with your ADC so she can’t harass and bully you.
Janna may try to ward alone in the mid and late game. If she does, try to ambush her by camping in a bush near the Baron or Dragon.
In team fights, Janna will try to use her Q and R to knockback/knockup enemies to delay their engage. If you need to get on to the enemy to kill them, be prepared to flank from the side to make it harder for her to anticipate your movements.
For AD champions, invest in an Executioner's Calling when Janna is ahead. This will reduce her healing and shielding capability on her allies.
Janna is very strong once she has a few points in her W. This can make it difficult for you to trade against her when she has her W available as she may come out ahead. Go for all ins rather than short trades.
Once Janna has her Ardent Censer, she is going to become really obnoxious in lane and look to poke whenever her W is available. Try to engage on her as soon as possible and do not let her poke you down.
Janna is always going to be strong once she has her R because it provides so much utility to herself and her team. Look to play hyper aggressive when she doesn’t have it available to increase your kill potential in lane.