As Kennen is a ranged champion, when playing as a melee champion, don’t let him poke you down with his Q or basic attacks. Be prepared to sacrifice some CS for XP.
Kennen has a versatile build path. Keep an eye on which build he is going for and build items to counter it accordingly.
Extended trades will benefit Kennen. Try to fight him when he’s low on energy or has no stacks to stun you with.
Kennen is really good in team fights. Avoid fighting in the Dragon or Baron pit as it will allow him to get a good Ultimate R off.
Kennen is prone to peel and disengage. Try to disengage as soon as you see him running towards you. Additionally, make sure you have vision to the side of you in case he tries to flank.
Try to harass and poke Kennen as much as you can before a team fight occurs. If you can keep poking him down, he will be unable to engage and fight if he’s low on HP.
Kennen’s power spikes depend heavily on the items he buys.
At level 6, Kennen will get access to his Ultimate R which is a great tool for him as it increases his kill pressure and his ability to trade with you. As soon as he activates his Ultimate R, run away.
Kennen is really good in team fights thanks to the AOE damage on his Ultimate R. Try and avoid fighting in tight spaces as Kennen will be able to deal damage to your whole team at once. Group but do not group close together.