An open floor plan can be decorated using contrasting paint colors. An example is painting walls one color and the half wall a contrasting color that compliments both colors chosen.
Create separate spaces using furniture and rugs. Define each area as independent by using varying seating groups. This approach is more useful than trying to create one big conversation area.
In terms of decoration, you should try to incorporate the half wall into the decorating scheme. Use the shelf on the wall to put plants with vines on, or decorative sculptures to help exemplify your design.
Be sure to keep the color palette consistent throughout the space. Use one or more colors throughout, and different accent colors within the divided spaces. The half wall is a great space to display items and books.