Use consistent, light colors throughout your home. While subtle changes can help distinguish areas, such as using different shades of yellow, don't drastically alter the shades throughout the home.
Keep the same schemes from living room to dining room to kitchen, rooms with functions that flow.
Create rooms by placing furniture in the right areas. For example, if your living room and dining room take up the same central space, you can use sofa and chairs as a barrier to define the living room.
You can use lattice-work screens or bookcases as walls.
Differentiate the decor in an outer bedroom or office from the main living and eating spaces by working with wall space and lighting. Give the rooms a focal point such as a painting and a distinctive light fixture or track lighting that you can direct in a way that contrasts in intensity or direction to the main living areas.
Embrace the amount of space you have, since too much clutter can defeat the purpose of the open floor plan. Utilize the outdoors by letting the light shine in, using outdoor plants as another form of decoration and by utilizing your porch as its own room.