The principles of design, whether it be accessories, fashion or any other area of design are color, shape, form, and function.
Color helps convey the overall mood. Brights elude happiness and joie de vivre. Dark colors convey mystery, sleekness.
Shape is the outline or silhouette of the product. Shape can convey ( but not limited to ) outrage, exaggeration, complacency, and strength.
Form refers to the manifestations of technique, embellishment, intricacy, detail, innovation, structure or texture.
Function refers to the to the intention of the object as well as the perceived manifestation of the designer ie. to keep warm, to hold, to surprise, to seduce. For all areas of fashion design, clothes -> accessories, interiors -> architecture or any other concept of design these principles must be addressed in order to succeed.