You can't leave Phuket before seeing a fire show!
The 2 best on the island are at Kamala, at Cafe del Mar, every friday and saturday starting around 6:30PM.
And the second is at Pine beach bar at
the intercontinental Phuket, starting at 7PM every night. Book in advance if you want the tables on the beach.
For night shots, the best is to bring your tripod, keep ISO 100, and select a long exposure at around 1 or 2 seconds. Need to test a few times before finding the perfect timing for your camera.