You can definitely mix stripes, but keep these two rules in mind: Stick to one color palette, and vary the width of the lines.
To buy: Lacoste cotton top, $160, shop.lacoste.com (available in late August). Loft cotton shorts, $50, loft.com for similar styles. Mango acrylic scarf, $25, mango.com. Nashelle bracelets, $63 each, nashelle.com.