Use your ult in team fight and for help in fights.so they take Damage and get stuned.so you can kill them easyer with your team.

What can I say, Magic Pen is Amazing for Kennen
The health per level will give you a-lot more benefit then straight health (past level 5) and Kennen needs all the survivability he can get
The ability power per level will also grant you a-lot more benefit then straight Ability Power (past level 5). Just helping him put out alot more damage, The only other blue rune i could see being decent is CDR, but it seems like a waste to me.
I've Tried Flat health, CDR, Magic Pen and Flat ability power Quints. I feel that 3 of these bad boys are AWESOME for early game, gives you that flat 15~AP that will help immensely for getting first blood. If you dont have the Flat Ability Power quints, your second best bet would be Magic Pen.

I like to go with a pretty standard 9/21/0 Build for Kennen, you will see most people going 9/0/21, but I believe Kennen excels a-lot from the Defense Tree. It gives you that little bit of survivability that really helps him a-lot.

I take amplifying tome so get ap and then buy mejai's soulstealer.
i take lonian boots of lucidity for cooldown.
i take rod of ages for health and ap.
i take rabandon's deathcap for more ap.
i take abyssal scepter.
i take zhonya's hourglass for ap and magic resist.

I stack THUNDERING SHURIKEN for heras.
Then LIGHTNING RUSH so it is easy to get away.
Then ELECTRICAL SURGE so i can stun more.

ts: for heras and to kill.
er: for stun.
lr: for running and killing/stun
ult: when they have a mark of the storm on them and when you ar in a team fight.

Use your ult in team fight and for help in fights.for Damage and stun with mark of the storm
on them.

Use ur lr for farming and then es and then ts for the last one.you should only heras and farm minuons not realy gank.and only recall when you need or at level 6.

i am making videos and there will be a montage on youtube in about 1 month hope you like it.plz vote upp not down and leav a coment.

comeing soon.