Void Staff if the enemy team are Magic Resistance stackers

Zhonya's Hourglass if the enemy team are doing too much dmg to you

Rylai's Crystal Scepter if you need some HP

Banshee's Veil if the enemy team are doing too much magic damage, or too much CC

It's really good to solo with lux.
start with lucent singularity, everytime your enemy is farming, you throw at him (and minions too, so you can farm aswell) and then auto-attack him. "why would I attack him if i'm not a DPS?" because of lux's passive. your going to take somethin like 50+basic attack+damage from lucent damage. it's significantly damage at the early game. one thing i use a lot is a combo that is really awesome: you hit your target with light binding, then throw your lucent singularity, but instead of just using your ablities, as soon your target get stunned, you attack him, then you blow the lucent singularity, and attack him again. thats about :50+basic attack+light binding damage+50+basic attack+damage from lucent damage. that's a lot of damage.

if you hit this combo twice, and your target dont die, you can allways ulti on him to get that kill. when your enemy realizes that your combo is that, as soon he get away from your light binding, he will run like crazy, that's when you use your ultimate

when you realize your enemys at top or bottom are with few health at tower, its really nice to ult at them, just to get a free kill.

light binding.
that's the ability you will use more.

get a lot the blue buff, and use alot light binding, at this point, you can't combo anymore, cuz you'll probally get attack or even ganked. so just stun and throw lucent singularity. this will hurt a lot your enemys and, your ultimate, in most cases, is just to kill that enemy that is running away.

light binding again.

a good combo is light binding+lucent singularity+finales funkeln (but really fast)

a good combo to enemys with low health is just light binding+finales funkeln

important to canstantly get the blue buff, ir really helps with its cooldown reduction and mana regen.

be careful.
your very squishy, so care on team fights, or even on 1x1, cuz if u miss your light binding, your enemy will rape u

constantly use your prismatic barrier, your friends and you, will be protected a lot of the time.

use your prismatic barrier in team fights, it really helps dieing friends and tankers.

the cooldown of your ulti is something like 30 sec. so use it a lot. you can ks with that but i dont recommend it.