The biggest mistake you can make when working with pastels, is pairing it with black. Sure, it's a fool proof combo and all that, but why play it safe when you can match it with other shades of the same palette and look like you stepped out of a fairy tale? Try lavender and baby yellow, Mint and light coral, Beige and baby pink, Mint and soft pinks...and there's just so much you can work with. That's the best part about matching chalky colors. They all sit together beautifully!
Another no-no when wearing pastels? Loud lips. Steer clear from red or anything dark. Light, natural shades are the better choice here.