Hi, welcome to my Lux guide. I decided to make this guide since I started winning contiuously with Lux.I was actually quite amazed on what she can do against tanks.

Pros
-Good Harrasser
-If used correctly, her snare will lead to kills
-Great Crowd Control
-can execute champs with her ult if aimed right
Cons
-Squishy
-Easily Focused if left alone

The Runes are based on my Offensive Ap runes which focus on magic pent and ap with Magic resist Glyphs to buff up against other casters.This is my Rune set every game I play Lux, but you can sub any of them if you feel as though they fit better.

Well as for the items, they are quite flexible. Morello's Evil Tome can be replaced by Mejai's Soulstealer if your team is clearly dominating. As for the boots Sorcerer's Shoes are the better pick for me rather than Ionian Boots of Lucidity due to the fact that you can grab other items which provide CDR and Ability power at the same time. But if you feel like the enemy's AD is getting strong or the enemy has too much CC feel free to switch it up to Ninja Tabi/ Mercury's Treads.

Pre Lvl 6 you can use your Lucent Singularity and her passive to quickly rid of the caster creeps behind.
Post lvl 11 you have the choice to use your ult ( Finales Funkeln)to farm as it has great damage by that point. it can kill creeps in one hit provided you have bought Rod of Ages/ Lich Bane by then.

Pre-lvl 6 save your mana for the moment you lvl up to 6. then go all out to kill, hopefully pre-level 6 you bought you Catalyst the Protector if not try to just basic attack creeps until you've got enough mana for two to three spell combos and save mana for you Finales Funkeln to finish off any who run.
Post-lvl 16 spam your Laser. it's half a minute cool-down and excellent damage allows you to farm huge creep waves from a distance, you can also use it to harass champs from a distance and lowering their health, provided you completed your Rabadon's Deathcap.

VIABLE
Heal/ Flash- NOW HOLD ON, HEAL? WHY NOT CLARITY? well i feel as though once you get your Catalyst the Protector ,you have enough sustain for mana, Heal for me is better than Clarity at some points cause what if you get ganked, Clarity sure get mana, no use if you get killed, heal on the other hand saves you from a like-wise near death situation.Flash-your escape mechanism,you could also use Ghost, it depends on which one you think is better.
Ghost/ Ignite- yeah escape mechanism and a kill securer, surely your team will get kills.
Ignite/ Flash- also a viable combination.
Clarity/ Flash-if you feel you'll survive without the heal :)
Clairvoyance/ Flash- scouting tool and escape mechanism, can help steal Baron or check bushes rather than facecheck them.
SEMI-VIABLE
Teleport-to easily def that lane left alone
Exhaust-to Increase chances of killing the enemy/also slow them down if they're chasing you
NOT VIABLE
Promote-WHY WOULD YOU EVEN GET THIS AS LUX, YOUR NOT A PUSHER, YOUR AN AP CASTER.
Surge- your not Teemoor Jax why get this?
Smite-you COULD get this what would you exchange it for? Flashor Heal

Always ask a team mates to baby-sit you early game, the experiences I've had in some games where they left me solo led to the enemy's AD carry getting fed. So having a laning partner,or the jungler ganking often will lessen the chances. But if you've had luck and managed to snare the AD carry by your tower when he/she dived you, finish them off if you can or just RUN back to base. AS for clashes I suggest you pop third as soon as possible to provide damage and slight slow,also use your Prismatic Barrier to shield your allies, snare the squishiest Champs with Light Bindingfirst, then release your Laser Finales Funkeln, that will probably lower their health to 50% if you've got a Rabadon's Deathcap or it might even finish them of.

Well with your 40% CDR with Morello's Evil Tomeor Mejai's Soulstealer combined with the Blue Buff on Summoner's Rift or Elixir of Brilliance your ult's CD will be 24 secs. That provided you'll have GREAT BURST if you got to farm and completed your items. IF not you still have burst damage and half a minute CD isn't that bad.
This guide is just how I play Lux,oh BTW just in case you dont believe me here's a pic of a ZERO death Lux, I was bot lane against their tank Amumu I kinda ruined his early game leading to their tank getting under farmed.,you can feel free to suggest which items I might switch out.Credits to my friends Lilarcor.Bot,Exl.Catclyst,Exl.btbtbt,TROLLSMILEand my cousinSnitchcloak who are excellent players and my clans The Exile, and Band of Terrors they were the ones who helped me test, evaluate, and improve my guide.
LUX-LASER TO THE FACE :)

-Still works up to current patch.
-Might swap out Morello's Evil Tome for a Deathfire Grasp in the main build in peeps want it
-adding a sub build after finals