This is my Kha'Zix guide.I'll show you how I toplane and jungle.Kha'Zix is my main and I'll show you a few Tipps&Tricks and especially how you win every Teamfight.This guide is made to escape out of bronze.

Unseen Threat (Passive)
When Kha'Zix is not visible to the enemy team, he gains Unseen Threat. Unseen Threat causes his next basic attack against an enemy champion to deal 15 / 20 / 25 / 35 / 45 / 55 / 65 / 75 / 85 / 95 / 110 / 125 / 140 / 150 / 160 / 170 / 180 / 190 (+ 50% AP) bonus magic damage and slow by 25% for 2 seconds. Unseen Threat lasts until consumed and has no internal cooldown.

Taste Their Fear (Q)
Range: 325 (375 with Evolved Enlarged Claws) I Cooldown: 3.5 I Cost: 25 mana
Passive: Kha'Zix marks enemies that are isolated from their allies.
Active: Deals 70/100/130/160/190 (+150% bonus Attack Damage) physical damage. If the target is isolated, the damage is increased by 45%.
Evolved :
Increases range of Taste Their Fear and autoattacks by 50. Additionally, Taste Their Fear now deals an additional 8% of the target's missing health as bonus damage (max 200 vs monsters). Against isolated targets this damage is increased by 45% to 11.6% of missing health.

Void Spike (W)
Range: 1000 I Cooldown: 8 I Cost: 55/60/65/70/75 mana
Fires exploding spikes, dealing 75/115/155/195/235 (+100% bonus Attack Damage) physical damage to all nearby enemies and slowing them for 20% for 2 seconds. Heals Kha'Zix for 40/70/100/130/160 (+50% Ability Power) if he is within the explosion radius.
Evolved :
Void Spike fires three spikes in a cone.

Leap (E)
Range: 600 (900 with Evolved Wings) I Cooldown: 22/20/18/16/14 I Cost: 50 mana
Leaps to a target area, dealing 65/100/135/170/205 (+80% bonus Attack Damage) physical damage.
Evolved :
Increases Leap's range by 300 and causes kills and assists to refresh Leap's cooldown.

Void Assault (R)
Cooldown: 100/90/80 I Cost: 100 mana
Passive: Each rank of Void Assault allows Kha'Zix to evolve one of his abilities, granting it an additional effect.
Active: Kha'Zix enters stealth for 1 second, gaining 40% bonus movement speed while stealthed. Leaving enemy vision grants Unseen Threat. Void Assault can be cast a second time within 10 seconds at no cost.
Evolved :
Allows Void Assault to be cast up to three times. Kha'Zix takes 50% reduced damage while in stealth.

I personally play Kha'Zix as a full damage assasin.As a full damage assasin I am able to shut the adc's with one combo out and escape with the E reset or kill another carry.Max Taste Their Fear first and evolve it first to get the full burst potencial.After that max Leap and evolve it as second to get longer range and the reset.

If you are playing toplane your Passive is very important.If you fight or harass try to have your passive ready. Unseen Threat activates when Kha'Zix cannot be seen by the enemy team, so you can reactivate it by using brush or Void Assault. Unseen Threat causes his next basic attack against an enemy champion to deals bonus magic damage and slow by 25% for 2 seconds.Harass combo:

Leap (E) jump on enemy -> Taste Their Fear (Q) isolated for more dmg -> Void Spike (W) and Autohit with Unseen Threat (Passive) for another slow and extra Dmg.

With the slow from Void Spike (W) and the Autohit with Unseen Threat(Passive) the enemy won't be able to chase you.The enemy will only be able to do one Melee range Skill/Autohit.That's why Kha'Zix counters many