Hello there!

My name is Néymar on euw and I'm here to teach you how to play lux. I'm currently platinum 5 and see lux as my best champion.

Pros

Great poke
High burst
Able to support teammates
Able to steal dragon/baron/buffs
Great range
Great siege/pre teamfight

Cons

Squishy
Easily assasinated
4 skillshots
Prone to jungle ganks

For runes I have always prefered as followed:
9x magic pen marks
9x armor seals
9x magic resist glyphs
3x ap quints

However, you can also choose scaling armor or magic resist. Best would be to create 2 rune pages, 1 with scaling magic resist and 1 with scaling armor. IF you're against for example zed, you choose the one with scaling magic resist and if you're against anivia you choose scaling armor.

Choosing ap marks is also personal preference. It allows you to have a slightly stronger poke early game but really hurts your damage as you build ap items. The base damage of your e is pretty high so I would recommend not taking ap marks.

For masteries see the tree above. Reason I take arcane blade is because on top of basic attacking with your passive, you also deal the damage of the masterie which really deals quite a bit of damage. I also took some sustain masteries because if you make 1 mistake against someone like fizz, you can loose quite a lot of hp and you don't want to go base all the time, because that would put the enemy in the advantage.

Shoes: For boots I take sorc shoes 99% of the time. Lux really needs the extra damage it gives. Another option would be to take cooldown boots, but I feel the build offers enough cooldown and if you get blue you have 40% already.

Athenes: Athenes if the perfect item on lux against every ap mid. It gives everything you need: mana, cooldown reduction, magic resist and ability power. Always buy this first unless you are against zed or have given a lead to the enemy ad mid, then buy zhonyas first.

Deathcap: Lux really needs her ap, and after you've got athenes and the passive from deathcap you have a lot of it. I recommend building this second to really start doing damage, unless you're behind and you need a mid game power spike for dragon fights. In that case buy void staff.

Zhonyas: Lux is a really squishy champion and if you get caught by someone like fizz or zed, you need that zhonyas. Also when you get hooked or get jumped on in a fight, activate this to survive untill your team helps you.

Void staff: Because lux does a lot of damage the enemy will probably buy some magic resist. Buy this to make sure not all your damage goes to waste.

Morellonomicon: This item is actually pretty good but I don't think it can replace athenes. Not because the base stats are bad, but because lux is a burst champion the unique passive isn't good at all. Also, it only gives 20 more ap than athenes and gives less mana regen and has no magic resist. However, you can buy it besides athenes if you feel you don't need zhonyas or dont need a defensive item or if you don't need magic pen.

Mejais soulstealer: Mejais can be a really good item if they don't have an assasin or a team with someone like thresh or blitzcrank. Especially if you do well you can roam around the map and get stacks. Your kit will make sure you don't die often, unless you make a big mistake.

Lich bane: Lich bane can be really good because it stacks with your passive. However, it's not always good as you have to come in basic attack range to trigger it, something you don't want to do if they have strong fighers (like irelia and fiora).

Deathfire grasp: Same with lich bane, you usually don't get in range to do it.

Defensive items: buy banshees if they have thresh, blitz or morgana or someone with a skill to pick you off. It is also strong to deny someone like veigar burst (because he won't be able to stun you). Buy guardian angel if you keep getting jumped on by 6 peopple in teamfights (zhonyas + ga = mad enemy talon). Buy quilsilver sash if they have zed and buy heart of frost if you need armor.

Illumination (passive0: This spell if great for early game harass. It's like a mini build in lich bane. Keep in mind that your ult also triggers this. This passive does not stack.

Light binding (q): This spell is the start of your combo. It is a root that travels further if it hits an enemy. Keep in mind that the second enemy hit takes less damage, but your passive will still be applied.

Prismatic barrier (w): This is a skillshot shield that you can throw at your allies. You will always hit yourself twice with it. If it hits an ally once it shields him, but when it travels back the shield will be refreshed. This skill does not apply your passive to anyone.

Lucent singularity (e): This skill is great for poking and does a lot of damage. If you throw it enemies that walk in it will be slowed and you grant vision of the area. When you cast it a second time it will deal damage and apply your passive.

Final spark (r): This is one of lux' signature skills. It fires a beam of damage in one direction. Because it deals a lot of flat amount of damage and has a high range, this spell is pefect for stealing buffs and objectives. Remember that it triggers your passive and applies a new stack of it.

Combos

Your standard combo will be q->first e->r->second e. This way, with a basic attack on the end, only one stack of your passive goes to waste. Also, you'll ensure that you hit your e and r because the target is rooted. Watch out for tenacity tho, because that can ruin it.

You can also make no stacks of your passive go to waste, but it will require you to do 2 basic attacks. Because that takes longer your target will be able to run away before you finish your combo. However, if you think he won't run away, you can do q->first e->r->basic attack->second e->basic attack.

Use your w whenever you expect to take damage.

Flash: flash is a must have on lux. Because you are very squishy and have no escape, you really need it to get away from tricky situations. You can also use it aggressively, but it makes you very vulnerable.

Ignite/heal: Manu people will think I'm crazy for picking ignite on a 10000 range champion. However, I play lux in a completely different style. Read more in the "early game" chapter. Long story short, ignite is better for getting ahead, heal is better for making sure you don't get behind.

Exhaust/clairvoyance: These could be useful in some situations but heal or ignite is just better.

Despite not having the best base stats, I think lux is really good at early stages of the game.
Try to last hit as many creeps as possible without having to use your spells. Especially your e costs a ton of mana. Save your e to poke the enemy, then go in with w to do a basic attack and trigger your passive. Once you hit lvl 6, try to hit an enemy with your q. Then do the first or second combo, described in the combo chapter above. You can also flash in for a last basic attack and ignite. Remember that basic attacks do decent damage early game.

tl;dr: use your e and passive to poke, at level 6 go in for a kill.

In the mid game your team usually groups to take turrets and dragons. Because lux is good at sieging and pre teamfights, you would expect her to do very good here. However, mid game lux is actually pretty weak.

Let me explain, mid game assassins deal just enough damage to kill you, but you lack the damage to 1 shot someone with your combo. You're still very useful though, so don't afk farm but help your team secure objectives and will fights.

When you have 5 items, have over 500 ap and have plenty of magic pen, lux really shines. Use q e r to 1 shot their carries.

Pre teeamfights:
Lux is really good at killing enemies just before the teamfight starts. When one of their squishys make 1 positioning error, use q e and r to instantly pop them. This way it's a 4v5. You can also use your ult on a squishy long before the teamfight starts, to make him half hp before it even start. He will either have to go base or fight with half hp.

When the fight finally erupts, throw your w on all your allies. Try to pop a priority target or hit as many people as possible with e and r.

I'll just write a number of how worried you should be if you're against this champion.

Ahri: 4/10 - You can poke her really hard early game and if you use q she can't ult, but if you get caught by a charm you're as good as dead.

Syndra: 8/10 - If you're against a syndra main that is platinum or above, she will always push you out of the lane at level 1 with her low cooldown q. Try to farm as much as possible so you don't fall behind. If you hit a q just throw your burst but don't come in range for a basic attack.

Anivia: 5/10 - Anivia's low base hp makes her easy to burst, but her egg form can be hard to kill. Don't underestimate her damage though!

Azir: 3/10 - Azir has a lot of damage per second but if you use w he won't be able to burst you quick. Burst him to win the fight.

Karthus: 2/10 - Karthus' low range and low start game burst make it easy for you to kill him. Don't stand in his passive too long!

Lissandra: 7/10 - Lissandra can jump to you and really hurt you. Stay close enough to your tower so she can't do that.

Malzahar: 5/10 - Your w pretty much denies is e. Don't get caught by his ult tho.

Orianna: 3/10 - You have a lot more range than her but her late game is very strong. Try to deny her farm with the help of your jungler.

Swain: 8/10 - Even though swain doesn't have great range, he can root you and really start pumping the health out of you. He can also sustain trough your burst with his ult. Try to poke him before you fight.

Twisted fate: 3/10 - He shouldn't be much of a trouble in lane but make sure to warn your allies if he hits lvl 6, and always ping if you don't have vision over him.

Veigar: 6/10 - Veigar's weak early game makes him easy to poke out of lane, but he can follow up on jungler ganks very well. Don't go too far near his turret. Also, watch out for his insane burst late game.

Xerath: 6/10 - Just like you xerath has a lot of range. The one who's better at juking skillshots or hitting them will win the lane.

Talon: 9/10 - This sneaky guy can kill you very fast, and with his e and r it's very hard to hit your spells. Farm with your spells and don't go too far away from your turret. When he goes off to roam, don't facecheck bushes when you follow him because it could be a bait. Same with other assassins.

Fizz: 8/10 - You can poke him early but don't get hit by his ult if he hasn't fallen behind because he can juke all your skillshots with his e and q.

Katarina: 5/10 - Poke her really hard early game so she falls behind. She shouldn't be able to kill you later on. Make sure you spam a lot of pings when she's gone.

Kassadin: 4/10 - His new ult costs a lot of mana and his burst won't kill you. Also his silence is removed. Make sure you follow him if he roams.

Ziggs: 6/10 - Same with xerath.

Brand: 5/10 - You outrange him but don't get hit by his q.

Riven: 2/10 - Just root her as she is trying to get to you. Just don't facecheck a bush she could be in.

LeBlanc: 7/10 - High burst and a skill to juke all your skills. Farm up to late game where you'll be more useful.

If you hit your q you will see the damage it does on a champion. Practice lux a lot and eventually you'll know exactly how much damage your combo does once you see the damage of your q.

Thank you for reading my lux build + tips! Make sure to add Néymar (on euw) in game if you want more tips.