Unlike some of the crazier nail art, nail contouring is easy to do and can be nailed (lol) with just one or two colours of polish. Just grab your brush and paint your nails in a neutral tone that matches your skin colour, and then when it's dry paint a thick stripe down the centre on the raised portion of the nail bed. Simples!
You can also skip the base coat and just do the stripe.
The optical illusion draws the eye down (kinda like wearing black on black), making your fingers look like they're #blessed with the longest and strongest nails EVER.