Lux is an op champion support, if you main playing her you will not find any difficulty against any other suppor or counters.
Takeing ghost will give to her a bonus of movement speed to chase or run.
since lux is very op with her poke abillities you dont need to take exaust or ignite.

Flash is an essensial summoner spell to take it might save your life or use for a combos.

Flash : like every other champion does. It’s particularly important and your life depend more on It, its the most important summoner spell which is an indispensable, you cannot not take it, you can use it to save your life, Dodge a spell cast or to protect someone on receiving damage that could kill him or to get closer to shield/heal him also to engage a fight.
Heal : This spell can be used to save a life when low on health and under attack. It is commonly used to get an early first blood by healing oneself for more than one's opponent expects. It is also a skill used for "baiting", where you make your champion appear weaker than it actually is to lure your enemies out of position or to get them to tower dive you. A similar baiting tactic is also commonly used with Barrier.
Barrier : is great for absorbing the burst of enemy champions or turret enhanced shots. Whether used on a squishy mid-laner or a tanky top-laner, a well-timed Barrier will help escape from tough situations.
Barrier is damage mitigating summoner spells, barrier is not affected by Grievous Wounds, has a shorter cooldown, blocks more damage (against a single target), and can be used while you're still at full health (good against 100-to-0 burst).
Exhaust : is used against the player that deal huge damage most are adc to slow their attack speed, attack damage and movement speed.
Ignite as your second spell if you think you can win your lane or can duel a healer champion in your lane.
Ghost You can take Ghost to save your life once you got catched by a gank, flash ghost and you are safe, or to chase someone.

Pros

Can provide shields for team with her W
Can build Support or full AP to help team!
Goes well with most ADC's if played correct
Good sustain in lane
Powerful kit that is easy to learn
Super good poke
Ranged ult easy assists
Powerful early
Good CC
Huge range on all of her abilities
Deadly combos is you land a Correct Q

Cons

Cons
Long CDR to cast abilities
May miss skills shots and be affected
SQUISHY
Decently immobile
Positioning is important
Mana problems early
Skillshot abilities

Passive - Illumination :Damaging spells mark enemies for 6 seconds.
Basic attacks and Final Spark consume the mark to deal bonus magic damage.
Weave auto-attacks between spells during the laning phase to maximize your trade damage and conserve mana.

Q - Light Binding : Fires a sphere of light that roots and damages up to two enemies in a line.
Throw this through a single front-line minion to root an enemy champion who thinks they are safely hiding behind it.

W - Prismatic Barrier : Throws her wand out and back, shielding Lux and any allied champions it passes through twice.
Pre-cast this during team fights to absorb incoming poke, aiming to clip as many allies as possible on both the outbound and return trips.

E - Lucent Singularity : Creates a zone that slows enemies.
Can be detonated manually to deal area-of-effect magic damage.
Your primary wave-clear and zoning tool. Use it to check unwarded bushes safely from a distance before walking up.

R - Final Spark : Fires a massive laser in a long line, dealing heavy magic damage. It simultaneously ignites and refreshes Passive marks.
Always cast this immediately after landing a Q (Light Binding) for a guaranteed hit. With its low late-game cooldown, use it freely to poke or secure objectives.

Lux plays as a long-range burst mage and zoning controller who dominates by spacing efficiently, harassing from safe distances, and securing key picks with crowd control.
Early Game & Laning Poke with E (Lucent Singularity): Use E to harass the enemy while securing minion last-hits simultaneously.Weave Auto-Attacks: Early on, proc your Passive (Illumination) by following up landed spells with a basic attack to win trades.

Manage Mana: Avoid spamming Q (Light Binding) aimlessly; keep it available to self-peel if the enemy jungler ganks or the mid laner engages.

Mid Game & Objective ControlFog of War Traps: Control vision around dragon/baron pits. Sit in unwarded bushes and wait for an enemy squishy to walk past.

Steal Objectives: Use the extreme range and high damage of R (Final Spark) combined with E to snip Dragons, Barons, or Rift Heralds from over walls.Side-Lane Waveclear: Instantly clear minion waves from range with an E + R combo when pushing or defending turrets.

Late Game & TeamfightingPositioning: Stand behind your front line (tanks/bruisers). Lux is fragile and has zero mobility tools once caught.

Shielding Allies: Cast W (Prismatic Barrier) through grouped team members right before major damage lands.

Picks over Tanks: Save your Q and full burst combo for priority targets (ADC, enemy mid laner) rather than dumping spells into the enemy front-line tank.

Core Combos
*Basic Poke: E (slow target) Auto-Attack E (detonate) Auto-Attack.

*Full One-Shot Burst: Q (root) E (throw, do not detonate yet) R (laser triggers passive + E zone) E (detonate) Auto-Attack (if in safe range).