Hello i am insaneswatage lvl 30 EU server:
Lux is my main and i LOOOOVE her.

well its a default dps caster dont really need to explain right?
i dont recommend anything else.

i recommend my default runes, and the quinteccenses are your own choice magic pen for late game dmg and ap for early game dmg.

These items are the best on lux the last 3 items are situational, guardian angel for protecting your spree and lich for more aa damage. (lich + Passive is amazing) Or a zhonyas for when you are getting focused.

In teamfights just shield your allies snare and slow enemies and ultimate when a low enemie tries to get away. Harras w/ your e then combo the enemie when he is low REMEMBER: E & Q when snared auto- attack once then activate your e to explode auto-attack again then ult and when necessary auto-attack. (if u didnt notice passive resets after every spell damage you do.)

This guide is not final any tips will be noticed and reworked.
I will add some more details and some more chapters about lux.

Happy lazering.