I thought it'd be helpful (and fun) to show you using pictures how to do it. Look really carefully, because it's very subtle!
(I decided to take these pictures on a whim, so please excuse my non-make-up'd face and my unruly hair. Oh, and I'm holding the iPad up and the camera was to the side, hence my side-gaze.) Here's my neutral expression, to give you a starting point of reference:
Here's me expressing "yes" - a slight eyebrow raise. It can be more pronounced, but it could also be even more slight than mine! (See what I mean, you have to really be attuned to faces?)
Here's me expressing "no" - a slight wrinkle of the nose. It can be a more pronounced wrinkle, or a slight one, but they both mean the same thing - disagreement.
Every day's a learning experience! Hopefully this will help you if you come to Nunavut to avoid repetitive conversations. :)