Hey Folks,
I'm an Italian player who played Hots since KT patch (love at first sight) and recently decided to climb up the ranked system in the time my studies let me play this game. I'm a former LoL player who evolved bored of that sloooooooow game.

KT was the love of this game for me, I climbed the ladder with him and I just love his playstyle, his concept and his set of skill. Kinda don't like the Charachter in the Lore from Wow tho.

Let's get started.

General Stategy

The key to play this KT is to understand when the phase of the game goes on and adapt your playstyle accordingly.

At the very beggining of the game you will play as a smart fellow. You should harras, when possible, the enemy in your lane with the D+W standard combo.
When your enemies go back to their gate, just put the bomb on the turret or wall.
Just remember to not use your Q on minions at this stage, never D it and focus on hitting the enemy player.
Another trick in this phase is to set the D+W combo on an enemy creep near an enemey player, the autospread will be reinforced by the inital explosion.
If you feel confortable you can roam and secure some kills with your amazing skillset. More often you should stay in your lane and force your opponent to go back to base.
Be aware that you lack mobility so be careful, the enemy will gang up on you and gank you gladly.
It's important to don't overexthend or wasting your E on an enemy you can't kill or force to teleport home.

When the game shift on the very firsts teamfight just stay in the backline and spam your D+W, while you can consider, based on the situation, to go with your W+E do help your mates to secure a kill or two. If the tanks or warriors approaches set fire to them with your W one or two times, their healt will be to low soon.
You can initiate a fight with a W+E but be careful to reposition yourself shortly afterward. Remember that you can now let follow you D+W with an autoattack, free damage!
The enemies maybe still ignore you at this phase, if not don't get killed and manage to stay oout of the brawl and save your E for potential assassins/bursters. Do not D your flamestrike.
harras with basic attacks whenever you can.

In the Late Game the strategy is really similar but at this point you will die 90% of the times (assuming your opponents arent blind or just stupid) and you will go NOVA. You have to throw at your opponents all the thing in your reportory as fast as you can smash the buttons. Phoenix should go first followed by as many W you can (D+W, W). Just keep hit them with basic attack cos probably most of them will have a living bomb attached. Do not focus, just it all the things that come within your range.

COMBOS

Obviously your D is the skill that empower all of your other skills. Do not ever combo it with your Q. Don't go around the map with your D activated, you never know which skill you will need at the next bush.

Your main combo with this build is to spam D + W. Your D will give you mana and health everytime you press it and will grant an awesome basica attack.

Another notable combo is the old D + E, basicaly it transform your meh cc into an awesome CC. I'd rather use it for defensive purpose and save it (or just the E). If you know a bunch of enemies run at you everytime, this can change the game. You will be alive, they will be dead.

LEVEL 1

I think there is no choice here guys. This one gives you a free sustain method and 4% abilty power on the top. Just awesome.
The barrier is far to weak nowadays and it's never worth it imho. You already have enough buttons to smash.
The Flamequest is just not for us, we will rarely use that fancy Flamestrike of theirs. We love living bombs.

LEVEL 4

Again, the D talent gives you free mana (in addiction to the Health from lvl 1). It's the most reliable way of recovering mana of all the three in this tier.
The other mana restore method is a gambit, you can ear it back with little benefit or you cna just lose mana. Free and guaranted is far better imho.
The other one is not giving you mana, instead it provides cd reduction on a single skill you have to use, and btw you will always need mana.

LEVEL 7
Bonus on our Flamestrike? No thank you.
Bonus damage on enemy that are likely to likely explode? Sounds overkilling to me, or not enough selfawarness.
Bonus attack for free after we use our most pressed key? Yay, thanks! This will add some more free damage to our mana free combo.

LEVEL 10
Based on the fact that in the late game you will be dead soon, I'd rather go phoenix cos it has no cast time and doesn't let you harmless in the process of casting it. Pyro on the other end can be golden versus heroes like Li ming or Valla, or just to initiate a fight.

LEVEL 13
You can go both CD reduction or Slow, it depends on what are you feeling at the moment. Personally I love the CD reduction, it let you spam your ability more often (like 2 sec reduction every sec if you placed both of your W).
Radius is not worth it versus smart opponents.

LEVEL 16
I just love the huge boost from the basic attack to your nuking damage. It also helps at getting objectives like forts, bosses, immortals and all the kind of thing you wish to kill. Oh and it awesomely fill the time you have you skill on CD.
Getting that extra D is simply not worth it imho, cos you are not going to place more than 2 W's before getting destroyed.
Bonus on our Flamestrike? No thank you.

LEVEL 20
Ult boost, no thank you, we don't need to replace it cos we are good.
Now you cna chose and you should look at the gameplay of your opponents. Are they often very close one to the other? Are they ignoring the Living Bomb? Just go for the infinite spread.
More often a safer choiche is the mana refill + ability power. If you can press it before you start the fight, it can work wonders.