We joined a bus tour, unlike the others, our guides Anja and Francesco were great. There were photographers, and not only they gave us loads of pointers, they were super enthusiastic and took care of us. I would highly recommend their service to anyone thinking of going to Tromso to see the lights.
Here are their details:
Arctic Guide Services - their facebook page.
Northernshots site where they sell the great photos they took each night.