None of this suggests where you should go, but hopefully help your chances once you have picked somewhere.
So earlier this year I was in Tromsø, and I got talking to a professionalism northern lights photographer who lives up there, on the flight from Oslo. He had some useful tips for trying to view them.
Obviously going at short notice is best so you can get the best solar conditions but flight prices often make that unrealistic.
If your just picking a date and hoping try to go as close to a new moon as possible the less light pollution the easier they will be to see.
Having a car certainly helps so you can pick where you want to go for scenery and or because you need to escape weather. It also gives you the option to stay out all night (make sure you have suitable supplies).
A lot of tour sites said the northern lights in Norway peak between 6pm and midnight - he told us this was not true (first time we saw them was 3am) .
If its cloudy keep driving into the wind (if you can) until you can see stars. Stop. Wait (we drove halfway to Russia). Also local weather maps should show cloud cover and projections for the next 24 hours.
The northern lights aren't always in the north, this I knew but a lot of people don't seem to.
If you're photographing them with a DSLR, your camera will likely pick them up before your eye does (If you want further information ask question on photographing the northern light).