As far as match-ups go, Lux is very hard to counter, especially because of her long range attacks and abilities. Katarina is one of the only champs that I have found to really give Lux trouble, especially after level 6. Lee Sin mid, as uncommon as it is, is also a slight counter, since he can easily sit behind minions and do all his damage, as well as dive you quickly. Although Ahri is said to counter Lux, knowing the range on Ahri's abilities and dodging them can easily reverse this. Talon is very tough for lux to beat because of his ability to close the distance between you and him with his silence. Finally, avoid going against Kassadin because he gets extremely scary after level 6.

For a complete list of who Lux is strongest and weakest against, visit http://www.championselect.net/champ/Lux .

With Lux's Passive, each time you land an ability on an enemy unit (champion, minion or monster), your next basic attack on them does bonus damage. This makes farming a breeze as you have great wave clear capabilities. Last-hitting is fairly easy to get used to, and if you don't spam your abilities, you should be able to get a lot of CS in no time. At and after level 6, you can use your R to grab a quick 6-7 CS and automatically reset or push your lane. This is nice because even if you use your ultimate and your opponent says "fail" in all chat, the cooldown is short enough that you can use it again when it matters. Make sure your jungler gives you the second and third blue buffs to allow you to lane easily, and keep both sides of your lane warded as much as possible to avoid getting ganked. This is very important because Lux does not have a good escape mechanism in her ability set, and burning flash is not fun either.

When your jungler ganks for you, like always you want to let your opponent push almost all the way to your tower. When you engage, you want to do a quick Q E combo, hopefully snaring the person and having your AoE slow right on top of them. At this point, your jungler should come in too, and you should auto attack the person to get the bonus damage hit. Then, activate your E to replace your passive on the person, followed by another auto attack. After that, follow up with either your R, ignite, or anything else you might need to secure the kill. With a good amount of CC from your jungler, a kill should be fairly easy.

Once you get your core items (Athene's Unholy Grail or Morellonomicon + Sorcerer's Shoes), you should be able to start roaming to top and bot lane to help out where CC is needed, while doing plenty of damage as well. Focus on getting blue buff as much as you can, pushing your lane, helping others, and securing kills and objectives.

Side Note: If your team decides to go for dragon, do not use your Q, as it will just pass through the dragon and not mark it, wasting your mana. Use E for damage and W to shield your teammates.

By this point, you should have lots of CS from using your Q E combo on minions as well as your R for instant wave clear, and you should have some kills from ganks, roaming, and dueling. If not, don't worry. One time in a ranked match I went 0/0/11 with Lux and still was doing loads of damage. But after your core items, work on getting the 3 major AP items, in this order: Rabadon's Deathcap, Zhonya's Hourglass, and Deathfire grasp. You need these to maximize your overall damage for late game teamfights and dueling. You may need to grab Zhonya's before Rabadon's if you are getting shredded by the opposing ADC, or "marksman". Once you obtain all 3 of these items, get Homeguard for your boots and a Void Staff to wrap it all up and watch people melt. I usually never get to this point as the game is usually won or lost before I get enough money to buy all of these shredder items. However, with a record of 11-1 with Lux in ranked, I assure you that it is definitely shredding time come late game.

Side Note: Late in the game, your R is like a smite, doing about 1000 damage to monsters. If timed properly, you are able to steal Baron or Dragon with ease, and your team will LOVE you for it.