Lux has great zone control abilities. Try to set up Lucent Singularity to prevent an enemy's advance or escape.
If you have trouble landing Prismatic Barrier, remember that it returns to you after it reaches max range. Try positioning yourself to hit your allies with its return trip.
Lucent Singularity is a great scouting tool. Try throwing it into brush before walking into it to check for ambushes.
Lux has powerful zone control abilities. Try to spread out and attack from different directions so she cannot lock down a specific area.
When retreating with low health, be prepared to dodge Lux's Final Spark, a red targeting beam fires prior to the main beam, so try to move to the side if possible.