Always go by weight, not height. A snowboard flexes under your body weight, so the manufacturer's recommended rider weight range is the most reliable way to find the right size. If you're tall but light, you'll want to size down; if you're shorter but heavier, size up. Height-based sizing is an outdated rule of thumb that leads to a lot of mismatched boards.
Where you fall within the weight range also matters. If you're near the upper end, the board will feel more responsive and snappy with better pop—great for aggressive riding. If you're closer to the lower end, the board will be easier to turn and feel more playful, which is nice for progressing riders or a surfy feel.
The biggest mistake is ignoring weight recommendations entirely and ending up on a board that's too soft or too stiff for you. A rider who's too heavy for the board will overpower it and get unstable performance; a rider who's too light won't be able to flex it properly.