This is my basic Lux build I've been using the past 2 days in ranked solo queue.

Your starting item is really up to you.
Feel safe without a doran's? Grab the meki or the Amp tome for your Fiendish Codex.
You rush the Codex, then pick up Boots 1, then finish of your Morello's.
Then come boots 2, cdr boots. With those 2 items and my mastery setup, you're CDR capped.
Offensive masteries 1 point in the utility cdr mastery is all you need, once you get cdr boots and the Morello's You have liek 39.62% CDR, which rounds up to 40%(max).

Once you get those 2 items, the build is VERY open ended.

Heavy AP team that focuses you? grab an FoN/Banshee
Heavy AD team that focuses you? Grab a sunfire/Frozen Heart
They aren't focusing you? Get a mejai's and go on a killing spree until they do notice you!

Anyway, using this build I have been rockin the DEMACIA lane with my friend playing Garen.
And let me tell you, Garen+Lux is rediculous fun and almost insta First-Blood
He goes Tank/off-dps, boots/sunfire/IE/CLeaver etc, ery unique build. Play Video
This song inspired me to start playing Lux again, I mained her for about a month when she came out!

Runes are pretty simple

I find that I have a lot of early game mana issues, so I'm rockin the 2 mp5 quints along with mp5 seals. These really help my laning harassment and control early on.

The AP/Magic pen is pretty straight forward. I like to use 3 Mpen Glyphs so if I pick up a Haunting Guise of Abyssal I pass the base 30 MR most champs will have.

9/0/21 Pretty Simple Ap Mastery setup, except for the Mana/CDR points.
As explained in the Intro, you only need 1 point in the utility CDR mastery to get max cdr with my first 2 items(CDR shoes and Morello's)

Skill Priority Varies game to game for me.
Sometimes I prefer to max E first, other times Q.
So its either this:
R > Q > E > W
Or:
R > E > Q > W

Either way, you do a good amount of damage and have great lane control/pressence.

I used to use 10/0/20 Masteries and use Ignite/Flash with a few different runes, and start with an Amp Tome. THis would give me insane AP early on.

But after playing a lot of ranked as Lux I've noticed I LOVE having the ghost+Flash combo.
It's just amazing on her, ghost allows me to catch up to runners to tag em with my snare or slow, or just catch them Blue pilling with my ult.

Flash, in my book, is a must have on any squishy champion. It's my favorite summoner spell right now.

Lux has amazing synergy in any team.

You ALWAYS want to be at THE BACK OF THE GROUP!
I mean WAY back. Your spell ranges are huge, so get just close enough to land your shield on your teamates, and jsut far enough to stay out of the enemies range.

It takes some work and mobility, but once you learn your positioning you will be extremely hard to get to, cc and/or kill by mid/late game.

Make sure you have a decent tank though, because if he gets out of position you can get dominated very quickly!

Make you sure you shield the right teamates as well! Don't let your MF with 100hp left die because you missed your shield on her! Throw it and MOVE AROUND!

I'll try to add some more details later, but I gotta go for now!
Ok so Mobafire says I need at least 5000 letters in my guide for it not be marked as spam. And I have no idea how many letters this is so far, so now I have to ramble liek this!

Peace 'n beats