Slender or Scaly Leaves

Scale leaves are often displayed in flattened splays or in a more boxy 4-sided pattern.

flattened splays 4-sided splays
Trees with single needles can be distinguished by how the needles are attached to the twig. Yew and Douglas-fir have tiny petioles (leaf stalks). Spruce needles grow on woody pegs. Firs have a swollen "suction cup" at the base of the needle.
petioles sterigmata suction cups
Pines have needles in clusters or bundles called fascicles. A quick and easy way to distinguish between the pines is to count the needles in the fascicle.
fascicles of 2 fascicles of 3 fascicles of 2 and 3 fascicles of 5