Typically, mannequins are used in a store as centerpieces for a specific outfit, the different components of which can be found nearby. This is a good way of using such visual merchandising tools, although others exist as well. For example, one could give a female mannequin a plain outfit, but use it to sell jewelry instead of the clothes it's wearing. Mannequins could also advertise hats or demonstrate unusual ways of wearing clothes that might otherwise clash. They could be considered experimental expositions of the style of the shop, showing ways that someone could dress in a sharp, extremely cutting-edge way.
It really depends on the store. Those places that are selling more conventional clothes should use mannequins to demonstrate regular outfits. However, for boutiques specializing in more outrageous designs, then it would be a good idea to use the mannequins to push newer and more interesting fashion statements. Putting such a mannequin next to some modern-looking containers, such as a zinc bowl, could give a certain edginess to the store that sophisticated shoppers might enjoy.
Another way to use mannequins that many companies haven't considered is for display windows at businesses that don't sell clothes. For example, a hardware store could dress a mannequin in heavy work clothes and have it pushing a rake to show the mannequin raking leaves. This will give more dynamism to a display that otherwise wouldn't have any people inside it. A grocery could show a mannequin in front of a fake oven or eating fake food from the store's deli case.
There are also mannequin alternatives, which typically consist of forms that can fit clothing but do not have the shape of a whole human figure. These are good for showing off clothes that could theoretically be worn by either gender, such as unisex jackets. They are also good for modeling men's suits because the appearance is a bit more formal than when using a typical mannequin.
Props and decor could also be used for a more formal look. Just remember to tone down displays and focus more on the clothes than the special event being highlighted. For example, showing suits in a window followed by a simple sign that says there is a sale coming might be more effective than multicolored streamers and balloons to indicate the same thing.
Displays that are not mannequins
Finally, there are displays that are neither mannequins nor alternatives, and they are usually reserved strictly for jewelry. Some of them, however, have the form of a human neck, and could likely show a scarf very well. Others, such as a bronze bracelet display, could have a scarf draped around them very effectively. Such a look would be striking, and likely effectively for something made of silk or another sheer fabric.
Remember to be creative with props. When people see something being used to do something it wasn't obviously designed for, people will remember it and think of the design as unique and worthy of attention.