As someone who was fortunate enough to see the northern lights in the lower 48 last year, this is good advice. Keep your eye on the forecast; unless you're far up north, good opportunities don't come along too often. Find a dark spot in the country with a good view, and be patient since they do ebb and flow. Although it can vary based on the space weather, your best chance is usually around midnight, and you can get frequent updates here http://helios.swpc.noaa.gov/ovation/
It took me a couple tries to finally see them the first time. And even that night, for the longest time, until my eyes adjusted, I thought I was just seeing hazy clouds. Every once in a while it would light up with color overhead, but sadly those only lasted a few minutes. Most of the time it was pretty faint, but still an amazing experience, and yes a long exposure is a must to get a decent photo!