Use paint to separate the areas. Choose two of your favorite coordinating colors, and use one for the walls in one area and the second where the rooms break.
Separate the spaces with furniture. Arrange furniture so that one grouping faces opposite the other area.
Install different flooring in the two spaces. Place carpet in the family or gathering room, and install hardwood, laminate or vinyl in the kitchen and dining areas.
Use area rugs to separate spaces, if one type of flooring, such as hardwood, is used throughout the entire space.
Add heavy crown molding, wooden or faux beams, or an archway to create a physical barrier from one room to the next.