Treatment of windows in your home reflects your personality and your design style. You can leave them clear without any covering if you are living in place with good and open view, but it is not good if you are looking in some average point, like sidewalk, streets or building.
If you do not prefer curtains or they are too boring for your taste you can cover your view in few very interesting ways.
You can use frosted glass which will bring you privacy but at same time will not hide you from light and view.
Window shades are rebirthing now using fabrics with UV light filter. Many of them can be programed to be raised and lowered without any efforts, but only with touch or remote controller.
You can use artwork in right dimension and position so it can bring creativity in your home.
Also maps, signs or posters can do the job and will bring you evening privacy and colored comfort in space.
For finish, you can use plants which will grow near or at you windows bringing you nature and various colors in your favorite place for enjoying.
Here you can find few ideas which can inspire you, so it remains on you to choose how you will protect your home from curious viewers.