Some people say nashor's tooth is useless on lux, well i disagree. I think it's very useful especially because it make farming a breeze when u can ignite her passive a lot faster. This also helps in team fights and chasing down single enemies. I get the sheen first so together with her passive u can dish out a nice amount of damage early game. Dont get soulstealer unless u know ur gonna get a lot of kills/assists. Replace it with an hourglass if u can but if u do, leave it towards the end of ur build. Also i get boots of lucidity because it helps a lot when i'm in between blue buffs. They may not give u the same amount of damage as the sorcerer's boots do, but i honestly don't really notice the difference. Other than that i think this is a fairly standard build for lux, but for me it gets the job done.

My masteries are standard spell caster masteries, except i added 2 points to buff duration because i find getting blue buff a lot really improves ur game.

Unlike the most popular builds for lux on mobafire i've gone for cool down reduction, health and mana regen. This way i find that i don't really have to spec for those in my build other than the rod of ages and boots. ap quints are good but i really don't like having only lux's natural health and dorans ring early game. Especially when u come across other champions that can harass just as hard as lux.

Get the stinger early on in ur build so when u throw lucent singularity into a minion wave u can ignite ur passive a lot quicker thus making farming a whole lot faster.

Remember this is just a guide on how to build lux, take different items to suit the your enemy. Also get blue buff as much as u can. Don't get too close to ur enemies, use ur range to ur advantage. You can initiate team fights, but never be on the front line. Your passive is ur real weapon, try and ignite it as much as possible. Other than that, just have fun with her. Good luck summoners!