Hey! :D
My in game name is WindCrimson (real name is Puck) and I am a Support main (but I like to play Mid once in a while). My favourite champion is Lux and I got more than 650.000 mastery points on her. I am not really high ranked (gold 3 solo/duo last season) but I would like to share my ideas about Lux and how you can play her!

Lux is just an amazing champ. I prefer long range champs because I am able to hurt the enemy before they can reach me. Let's take a look at the positive and negative sides of Lux.

Posivite:
She has a long range
She has a low ult cooldown
She has a root, a shield and a slow
(She has nice skins XD)

Negative:
She is really squishy
She can't really do anything at melee range

This part will be split up in two smaller parts called "How to play Lux Mid" and "How to play Lux Support", even though there isn't really a big difference.

How to play Lux Mid?
The main thing about playing Lux Mid is: "keep your distance". Just harass and poke untill the enemy is low enough oneshot them with a Q --> E --> R combo. Don't forget to ward, if you get ganked by the enemy jngl with your noticing it you will be dead for sure.

How to play Lux Support?
As you may have noticed, my Lux Mid and Lux Support build isn't that different. This is because I think that Lux is just made to get kills and get fed. So when you play Lux Support, try to 'share' kills with your ADC. Let him get fed but don't forget yourself. Try to poke a lot in the early game for the Support Item Quest. Warding is really important so try to get that one as soon as possible and change your normal wards to Oracle lens.

In both lanes, just try to rely on your Q --> E --> R combo, especially when you get fed. If you are really really behind, just play safe and stay in the backlines and try to get some kills or assists without taking too many risks.

I am not gonna explain every single rune, so I will just give you guys a quick overview.

Why no Aery in the Support build?
This is because I prefer more damage and poke over a really really small extra shield and less poke and damage.

First Zhonyas or first Banshees?
This depends on the enemy team. If there is an ultra fed AP champ, go Banshees first. If there is a fed AD champ, go Zhonyas.

Why buy the items in this order?
This is because I love cooldown, so I always buy the cooldown items first.

Why Ignite and no Barrier?
I prefer Ignite over Barrier because I honestly forget to use Barrier when I am in a battle (but that's just me, I guess XD). Apart from that, I just like to have a last resort when a melee champ jumps in my face. Like, when a Talon jumps in your face, you can root and ignite. Maybe you will kill him, but if you don't you will deal a fair share of damage, so he will probably head back.

I hope I helped some of you out there with some nice Lux information :). If this Guide didn't help you or if I wasn't clear about something, you can always ask me about it.

Have fun playing Lux, byeee! :D