So I have been playing League for about 3 months now, and I have tried almost all the champions, and I seem to have fallen in Love with Kennen.
I read a lot of guides on here, and it seems like everyone says *BEST CHAMPION ON MOBA* well... I'm not going to tell you that, but I will tell you that Kennen is fun as hell to play, and once you learn him, he definitely can tear up some people.

Like every other champion, there are a few ways you can build them, I personally like building my Kennen as AP. There are a few things that I do that i believe set me apart from a few other Kennens, and I like to think it's what puts me ahead of the other players.

I use the runes showed up there and now I will explain why:

Marks: As you can see I use Greater Mark of Insight. Not much to say about them, they will help you early game and can work well late game but nothing too much.
These are the only marks I every tried using for Kennen since they are good and everyone uses them.

Seals: I love using Greater Seal of Force because they are just awesome, well you will feel the impact on your ability power early game but they make up for it after LV6.
There are some other runes you could be using depending on your play-style:
Greater Seal of Vitality <-- I have been using those for quite a while but I figured I don't need them actually and I like to focus on the damage output since you get enough health and resistances from your items. If you ask me 2200 health is quite good on a squishy ability power champion.
Greater Seal of Potency <-- These I don't use since I focus on late-game team-fights and not early-game ganking, I suppose these are quite good if you want to end game quickly which will usually not work in ranked games.

Glyphs: As you can see up there I am using Greater Glyph of Force the description is the same as with seals and it really does not make sense to repeat something one hundred times over and over again.
You can also use:
Greater Glyph of Potency <-- As said earlier I focus on late game so I do not prefer using these but I suppose they are quite good, since they work well on other AP champions...

Quintessences: Here I obviously use Greater Quintessence of Insight since that Magic Penetration comes in really handy and is good through the whole game.
You can also use:
Greater Quintessence of Fortitude <-- I have been using these for quite a while, awesome runes indeed, great for early game, but if you take Doran's Shield as first item you don't really need them, sure extra hp is nice but you have enough even without them...
Greater Quintessence of Force <-- These are the only ''per level'' runes I do not prefer using since they become better then flat AP runes on LV 12 which is too late if you ask me, sure I do focus on late game but these just aren't worth the trouble.
Greater Quintessence of Potency <-- These are the only flat AP runes I would choose using since 3x of these grant you almost 15 AP at LV1, which is really awesome if you ask me.

As you can see I use Flash and Ignite.
Ignite will cover the little bit of damage you are missing early game, while in late game it will mostly be used to severely reduce enemy healing spells such as Mundo's ultimate and Olaf's Vicious Strikes.
Flash is my favorite summoner spell.
It has saved me countless number of times from ganks. In combination with Lightning Rush it can be used to escape from team fights if you get to low on health. Not to say how awesome it can be for running from enemies in the jungle since Flash enables you to pass through every wall on Summoners Rift.