If you want to maximise your chances of seeing the incredible northern lights, then a tour is a good idea. It can take some skills to get to the right area at the right time to spot them. So going with an experienced guide will increase your chances of seeing the lights.
I recommend to join the small group tour with Arctic Adventures. They have great guides and in case you don't see the lights, you can come back for free the day after.
Another really fun option is to do the lava tunnel & northern lights combo. The lava tunnel is massive and makes for an really fun adventure, even if the lights don't come out.
Remember to always dress warm and enjoy the show!