I bought Kennen a while back and have just recently figured out my own take on being successful with him. His main weakness is that he's 'squishy'. You can get by this is you constantly harass them by bursting in and out with the Lightning Rush and Electrical Surge combo.

Alternatively, you could stay at a safe distance and keep hitting them with Thundering Shuriken.

Thanks to some helpful tips and comments, I've chosen to update this guide to a better standard. This is just an idea to how I like to build Kennen.

I'm not up to level 30 yet myself, so I haven't got the Archmage , Arcane Knowledge and have only 2/4 on Sorcery at the moment, but the Mastery Tree I chose would be what I would probably have at that point.

Alternatively, you could swap out the 3 points of Vampirism for 3 points in Resistance for that extra bit of magic resistance. Remember, this is just a guide, so give your own personal little twist on it, if you like.

For runes, I would either suggest flat AP or gradual AP for most of it, with your runes filling the Magic Resist part. Again, alternatively, you could go full out AP, or full out Magic Resist. It boils down to what you're used to playing, or what you think would be more suitable to the commonly played enemy champions.

I usually start with the Amplifying Tome for the First Blood start of the match, then proceed to get the Mejai's Soulstealer. This item is brilliant with Kennen or any mage for that matter, because you don't have to aim for the kill to gain extra AP from the stack, just an assist.

Going in order, I'd get the Boots next. Now, depending on who you're facing, I will almost always get the Sorcerer's Shoes. The magic penetration from this will near enough cancel out any enemies who choose the Mercury's Treads, of course, your abilities could always use that extra penetration regardless.

Rylai's Crystal Scepter is next and this is another brilliant item. It gives you a trio of goodness. 80 AP with 500HP and your attacks can slow enemies, very useful indeed.

Rabadon's Deathcap. For obvious reasons for any AP build. High AP increase + 30%. Marvelous.

Abyssal Mask is a great choice, especially if you're against other AP champs. Then again, with the 70 AP and it's aura, always a valid choice.

Finally, the Zhonya's Hourglass. 100 AP with some defence to beef Kennen up a bit. This is on your recommended list purely for it's active ability, which you should activate straight after charging in with your ultimate Slicing Maelstrom. You'll remain damage-free for a couple of seconds whilst your skill fries the enemy.

Other items I would consider depending on your enemy champs;
Wit's End - to beat down the mages
Will of the Ancients - If playing with other mages
Malady - It's passive makes your basic attack get a bonus, could be useful
Void Staff - More penetration if your enemies are stacking resistance

I start with the Shuriken for 'first blood' then get at one of each of the others. Levelling up, focus on getting your Electrical Surge to level 5 first, then your Thundering Shuriken, whilst of course getting a skill of Slicing Maelstrom at levels 6/11/16.

If you use the default "Q-W-E-R" for your skills then this'll be easier to explain how I sequence skills in champion fights. 'A' = standard attack while your skills are on cooldown.

Single Enemy; Q - E - W - aaa - Q - W - [E] (if they're not dead already or you're losing health, make sure you have 'Ghost' or your 'E' skill available)

2 or more; E - R - W - Q - aaa - Q - W -E

That's the jist of it, but you'll find out what sequence best supports and benefits you as you play Kennen more.

I tend to use Ignite hence me using Summoner's Wrath in the mastery. Ignite is a wonderful finishing spell for those low health enemies who think they can escape "the flippin' ninja", Kennen. It gives you 5 extra AD and AP, which is always useful.

I would suggest either of these for the other spell;
Ghost - for chasing or running (of course)
Flash - same as above
Heal - for your time of need or help your teammates. (warning: may cause foes to call you 'heal noob' on chat ;] )
Demote - not one I would use myself, but it's slowing and weaking effects would be good for giving the finishing touch to fleeing enemies

The easiest sequence to use to farm creeps is to run through as many creeps as possible with your Lightning Rush, then give them a blast from your Electrical Surge and hit the one with highest HP with your Thunder Shuriken. Continuously repeat this little sequence and you shall be racking up the minions kills whilst reaping all the bounty for your item build.

Jungling is another issue altogether. Since he's regarded as 'squishy', and would prove to be so, I would recommend sticking to farming creeps until you're built up enough.

This is usually around level 9/10, when you can start taking on the buff reward monsters and ,unless with at least 2 allies, (or champs like Warwick and Fiddlesticks), you should be around level 14-18 when attempting to solo any of the bigger beasts.

Being an energy user if so very advantageous with creeping/jungling since you don't have to keep returning to base to top up your mana.

However, if you have around 200+ Ability Power before such a level then just go for it. Just make sure you can escape safely without dying if it starts going badly.

This one's simple. You stun the hell out of the enemies whilst your team mates take most of the aggro. If you're a quick hitter, you can blast out 2-3 stun within 10 seconds to multiple enemies.

Team work is dependant on how well your allies can play their champions or perhaps it would depend more on how well you can communicate. If you happen to get team mates that aren't able to speak your language, then a simple single ping at a location on the map might be of assistance.

Please try to refrain from spamming the map with pings.... it can get so very annoying.

I hope this guide helps to give you an idea on how to use/build/stack Kennen and hope you have some good games with this fun-to-play champion.

I've added quite a few changes, due to my own change in preferences as well as the feedback received from the comments section.

Thanks very much, if there's anything else I've missed let me know.

Good luck, have fun and good day to you.