You know that clashing is a no-no when it comes to your personal style and that of your store, but matching isn't always an all-encompassing "do," either. There comes a point when display tables and store window visuals can become too matchy-matchy, and it's up to you to be able to tell.
One thing that should always match is the theme of your displays. For instance, if you are creating a display of mannequins, they should be wearing outfits that generally mesh well together. If black-tie is the theme, don't put one mannequin in street wear when the rest are wearing gowns.
Colors can get particularly tricky. Unless you are featuring a specific color for the month or say, having a sale on all things yellow, an all-yellow table can be overwhelming and not visually pleasing. If you still want to keep things relatively simple, add some hues that are nearby on the color wheel, such as green or orange.
Matching prints everywhere can also be unattractive, and having too much of one print in one place will not showcase its special aspects. Adding a bowl of zebra-print bracelets to an otherwise red and white display would add an interesting visual, but imagine an entire display tables filled with zebra print clothing, jewelry and shoes? It would become repetitive, and probably detract shoppers rather than attract them.