Oversized scarves create a contrast: the person wearing it immediately looks dainty and fragile.
Monochrome and tartan work well. If you are going for tartan, it has to be large. A small print would clash with the size of the garment.
These scarves also look particularly well with leather jackets.
Colour-wise it’s good to use softly contrasting colours.
A cashmere oversized snood or scarf is also great for a more understated look. Once you wear light grey (undyed) cashmere, you send out a signal to all the fashion aficionados: you know what’s good.
A little bit harder to wear, but for extra chic you could go with the silk variety.