Regular

DoubleJumping is one of the main reasons peopole main Kha'Zix. Doublejumping is when you E and kill someone midair and then E again before you land. This is so good for reaching the enemy backline in teamfights. For example: their Jhin is far behind the others in his team and he decides to ult. You are too far away from him and you cant just run through their fronlinte like an idiot. Leona who is in their frontline is at 20% health (400 hp) and you know that your Q deals 500 dmg on her. The only thing you can do to get to their Jhin is Doublejump. You jump OVER Leona, not ON Leona, Q her mid air, gets the kill and right before landing you use your E again to jump on Jhin and oneshot him. He was all the damage they had and with the E reset you got from Jhin you were able to jump back to your team and help them out in the 3v4 that's left(let's say your toplaner died). You won the fight and its a free Baron + mid inhibitor. If you DIDN'T doublejump you wouldn't be able to get to jhin in time and he would have gone banans and get kills left, right and center. And you and your team would lose the fight, Baron + mid inhibitor. This would only occur if it was a high elo ranked game where they bully you for the smallest mistakes, in lower elo(bronze, silver and gold) it's not that big of a deal.

FadeAways

A fadeaway is a type of doublejump but it's a bit different. It's when you stand INFRONT of the target and jump away from it instead of standing behind the target and jumping over it. This needs skill and a lot of practicing.

Skirmishing earlygame

W > Q > AA > R > AA > Q > R > AA. And they SHOULD be dead. This one is for fighting skirmishers mainly.

Oneshotting carries

Edge of night > W > E > Q > Tiamat > AA > R > AA > Q. Edge of night is good vs Tristana and Vayne who is just going to ult you and jump away.

NEVER try to 1v1 someone if they aren't isolated or if you're behind.