Use and combine patterns just as you do with your clothes. Normally, floral patterns look better together, as do geometric patterns. Medallion centers draw your attention to the center of the rug. Floral spray designs work well as background color and don't draw attention to the rug. Floral designs go well with Victorian furniture and 18th century stylized furniture.
Geometric designs are best with informal looks, heavy woods, pine, maple and leathers.
Oriental rugs of the same name may not be of the same quality. Similarly country of origin does not define quality. Old or used rugs are often abused rugs dressed up for sale. Avoid auctions, unless you have an expert to guide you. Beware of sales and beware of original prices or discounts which seem unrealistically high.