Lux... is my absolute favorite. This Lux build is all about becoming unstoppable. Guarantee that if you once you get this full build, your enemies will start dropping like flies.

Pros:

• Lux can spam her Ult with enough CDR
• Lux's W gives her enough bulk that she can outlast most opponents
• Lux's main damage spell (E) also slows the opponent
• Awesome CC that also does decent damage

Cons:

• Early game Lux can suffer some mana/CD issues
• Easy to get over confident and try to take on entire teams alone

These runes are pretty standard for APs - AP and Magic Pen to hit harder, and armor to survive longer, since in bottom lane you'll prob be facing an AD carry.

This is almost the standard Lux build, with one minor tweak - I put an extra point into offense instead of putting 9 in utility in order to extend buff duration. You shouldn't have to depend on Blue buff as Lux, no matter what the other guides tell you.

• Athene's Unholy Grail: Absolutely standard on every Lux build. Gives you the Mana Regen and CDR you need to be able to hit off your spells nearly non-stop.
• Sorcerer's Shoes: Duh. Build these second, you need the Magic Pen more than the CDR.
• Deathfire Grasp: Give AP, more CDR so you near the cap, and has an awesome use ability that can give you that extra damage you need to finish a kill.
• Rylai's Crystal Sceptre, Rabadon's Deathcap, Rod of Ages: I usually build Rylai's before Rabadon's for the added health and survivability so that you can stay in lane longer, but it doesn't really matter which of these three you build first - go with what you need.

First off, Lux's E is her main damage source (at first), and a great harass. Because of her passive and the good range of this ability, Lux can not only farm but also keep the champs opposite her running.

Next, Lux's Q - her main CC, but also does decent damage as well. It's easy to use her Q to set up hitting your opponents with E, just make sure to auto-attack in between launching your second skill in order to fully utilize her passive.

Lux's W is great, but doesn't see much use until late game: You should be harassing your opponents enough that this skill only has to be used to avoid getting ganked/to save fellow teammates. Later on, this ability contributes to the bulk that you build - and it will have such a low CD at that point that Lux will rarely have to worry about taking on anyone 1v1 or even 2v1 at full health.

Ahh, Lux's Ult. Now this is a thing of beauty. Once you ding 16 you should have both Athene's and the Deathgrasp: so the cooldown on Final Spark should be close to 30 seconds. Don't be afraid to spam this ability - it's great for sniping champs running with barely any health left, it can be a good deterrent to champs chasing after you for the kill, and it's a good way to open up a team fight. Yeah, that's right - because of the low cooldown, you'll want to open up large team fights with this ability, and then use it to finish off anyone who got away from your group alive. It can even be used to snipe Baron or one of the other buffs from opposing teams who think they have it locked down.