The best practice for dining room rugs is purchasing one large enough to fit your entire dining set, even when the chairs are pulled out. This will anchor your space, but also keep from legs getting stuck on the edge of the rug or the rug curling up over time.
If you have a rug you love, but it's too small, we highly recommend layering. Purchase a larger neutral rug that is both complimentary to the space and the smaller rug. Place the neutral rug (something like jute) underneath and place your
area rug on top.