Here's a tip: It helps to know exactly what you're looking for... The Aurora Borealis has (as the Inupaq say) two 'personalities'. There's the one you see on TV and in those spectacular photos; veils of rainbow colors rippling in the sky. The other one is much more subtle and can occasionally be seen as far south as Northern Oregon. That one is a faint and shifting green glow, the color of glow-in-the-dark plastic toys. It resembles cloud shapes and will fade in and out very slowly.
Of course, as PEB stated, it is much harder to see when it's not completely dark out.