Even veterans in home design sometimes have trouble when it comes to decorating large windows. It can be difficult to choose the appropriate window treatments for such large panes of glass, because issues of scale can be much trickier.
Depending on the aesthetic that you're attempting to achieve, however, it is possible to get the look of window treatments right even on your big windows.
By far the simplest of the options for your big windows is a drape. These can hang from a rod that spans the entirety of the window, sitting at either end. Whether you choose a pattern or a solid color depends on you and the look that you're trying to achieve in the space. If you're dressing a particularly expansive window, it's recommended that you hang the curtains a little outside of the frame, and that you use more than one drapery panel, so that there is a convincing amount of fabric to the side of the window.
If you're looking for privacy as well, you might want to choose something a little more involved. Sheer drapes work very well to conceal the look of a room to the outside but still let in light. Many homeowners have had success by hanging sheer grommet drapes over their windows, finding that they provide sufficient privacy while also adding a chic look to the room they're decorating.
If you're looking for a more formal strategy, or are dealing with windows that are interestingly shaped, many people have had good luck by dressing their window with valances. Hang these across the entirety of the glass to finish off your room in an interesting way.
Large windows are a real asset to any home, and once you've figured out how to finish yours, you'll love them even more.