Yep, look closely at the needles. Fir are flat and spruce are square. Roll them between thumb and forefinger, (like the way one would hold a joint), fir needles don't move much, spruce spin in your fingers.
The one that's easiest for me to distinguish / ID is Douglas Fir. Aside from the color of the needles (they're a dull aquamarine-ish color, nice), they smell like lemon-orange.
They're single needles, too... no ?
I'm so allergic to Spruce that I get nauseated when I'm working with them from being picked by the needles so much.
Fir's foliage, when crumbled in your hands, smells like lemons. Spruce smells like your typical x-mas tree.
And as said above Fir is F for Flat
Spruce is S for Square. In our area theres only 3 really. Fraser (which arent that common mostly planted), Balsam, and White. You will see SOME Dougs but they were planted. Balsam and Fraser have a REALLY smooth bark, Whites have long flat needles that almost look like a blue spruce. Frasiers are a lil tougher, as they look identical to Blasam, but they are so rare up here, unless planted..................