These are the builds i use while playing Lux AP/Lux Support.
I'll keep it short.

For Lux AP I did full AP runes, I chose the ones that would end up giving the MOST AP by level 18. This does make a great difference in you final AP score, these runes will end up giving you 50+ extra AP by level 18.
For Lux Support I did some armor and quite a bit of mana regeneration. I went for the Greater Replenishment Runes because you can't wait until level 18 for a few extra points of regeneration, you need it now. I added a few Marks of Resilience for armor, and Quintessence of Clarity for those few extra points since the Replenishment runes did the trick for beginning game.

For AP Lux you're going to want to follow this build to help keep you in lane longer while still being able to harass. The many points in offense makes this AP Lux A bomb (She is promoted to a Nuke after you buy the items, of course) and the very little points in utility help her stay in lane longer with mana.
For Support Lux I put a bit into utility for extra mana regeneration, larger sight ward ranges, more gold, and extra cool down. The small amount in defense helps you more than you might think beginning game.