Kha'zix is a strong melee champion with high utility and damage, he's great at targeting one weak enemy and eliminating them before jumping back to safety. The early game can be hard agains any melee champion that have a ranged ability even though marksmen should be easy to take out because of your big gap closer.

Try to get your opponent poked down to about half health in the early-mid game. This way you can do a E,W,Q combo which will eliminate them really quick. I recommended Teleport because khazix is a very mobility based champion that requiers to be quick and mobile. You can use ignite for a safer laning phase but it will not help you in the mid-late game when teamfights starts and you have your E evolved. Make sure not to start a teamfight but rather wait and sneak around the enemy team to get the ADC and other weak players before the fight even start. Kha'zix can jump over a wall and drop a enemy right in front of everyone and still make it out fast by having a evolved E so he can jump right back(E CD restet if you get kill or assist)