The mask works best in environments with temperatures around 70°F or lower, as you need warm/cool air to activate the shift. Your warm breath fades the ink to transparent; cool air darkens it producing a moving effect.
Some people even opt to carry around a damp napkin and subtly wipe their mask to keep it faintly moist. It reacts to subtle breaths better in that state.
If you own two or more masks, you can privately switch masks and keep the effect "new" for the people around you.
And lastly, perhaps most importantly, do not store your mask in sunlight for long periods. UV light harms the thermochromic ink and renders it permanently static.