Early game (Pre-4) you'll want to level, Start with Golems, then Raptors, Then Red Buff, This should give you enough time to get 2 levels, Maybe 3, This is the right time to gank either Mid or top, Depending on how they're pushed, If neither are pushed, Head up to the rest of your jungle and do a clear.

With Kha'zix you need to remember that you're based around isolation so if you're confident in your playing, Go for an invade or gank a solo lane, Or wait until the enemy adc backs off and leaves the support as a nice treat, But remember not to get too cocky and try to gank when they're pushed, As Kha'zix you can easily be taken down by any mid-level CC (Brand/Braum/Janna) and shut out, It's best to gank top as most of the time this lane is warded by your side and can easily be pushed in

As Kha'zix you can afford to get a little cocky once you've put your first point into your ult as you've got a form of escape combination with your Leap, Remember though, You only get one charge so use it well.

Losing out? Build hyper tanky, With Kha'zix you can add in a small amount of damage through Dead Mans Plate or Titanic Hydra, And still be relevant, But if you do end up getting a nice lead, Use it, Take Assassin's Items and punish them for being out of position and being out of place in teamfights, Main point to remember is: ADC>Mid>Top>Jungle>Support (Unless you know, Their Support is Support Zed/Yasuo >_> )