We saw them in Iceland during the first week of November.
Did a small tour, minibus, they only operate when there is a chance of seeing them, not guaranteed even if a clear night. Glad we went with them, as although more expensive, we saw the other tour operator, all 3 coach loads of them, parked up waiting - and they never actually saw them - we overheard folks taklking at breakfast the following morning.
After 4 hours of driving around at midnight and just when the guide was going to give up they came out. We parked up on a snow clad hill with the black star studded sky above broken by the dancing green lights. Absolutely magical. Don't bother with trying to get photos just watch. You can buy books with better photos than you can take.
Check the moon phases as they are brighter when there is no moon.
Good luck and enjoy.
Rob