Hello! my name is M3GUSTA and this is my first build so please be friendly ^^....
khazix to me is a "clean up" type of champion.. his role is to burst down the ad/ap carry or finish off the low hp champs who are running away. As for runes and masteries... i usually play khazix with flat ad runes and masteries.. i usually focus on his ulti> first skill>second skill>third skill...the purpose of his ult is to reduce focus on him and to make a clean getaway.. i hope people would teach me how to work with the masteries/skill distributions on this site

Void ***ult(R) > Taste their fear(Q) > Void spike (W) > Leap (E)

i usually use his first skill to farm but not excessively just enough to get me enough cs for each wave

as for teamfights is wait for the tank to engage and im usually the second last to enter the fight to clean up or burst down the ad carry..