Defining a space: If you have an open area dining room that shares a space with a living room or kitchen area, an area rug will help you define the dining room without using walls. Choose a rug that uses colors from adjoining spaces but still defines the space. Therefore a mixture of neutrals from the surrounding rooms with a punch of an accent color to match the dining room chairs would be perfect.
Choose a pattern or not: In some dining rooms the area rug serves as a floor covering that feels good underfoot and is meant for function and not décor. While other dining rooms keep a simple table and chairs, and then have the area rug take command of the room. If you choose the more bold approach, choose a few colors from the carpet and bring them into the wall color and fabrics of the room. This will unite the room and keep it from looking too busy for the eye.