The most common look for layering rugs seems to be an animal hide (faux or no) over a sisal — this is probably the most neutral option. Other examples mix patterns and colors, sometimes creating a bohemian wonderland of textiles. Dusty, perhaps, but cozy and romantic!
1 Jenna Lyons layered a zebra hide over a Beni-Ourani rug, photo by Melanie Acevedo for Domino, via Bride's
2 Floral over plaid in this room designed by Jeffrey Bilhuber, via the decorologist
3 Layered Oriental rugs lend an air of mystery, via Matters of Style
4 Layered rugs keep this garden room feeling cozy, via Sara Says Awesome
5 Eclectic patterns layered in this room featured in House to Home, photo by Paul Raeside
6 Mixed stripes in the bedroom chez Lisa Maycock of Vena Cava, via Design Sponge
7 Nicole from So Haute layered a neutral hide over a neutral sisal, via Apartment Therapy
8 Mismatched oriental rugs serves a wall-to-wall carpet in this room, photo by Tony Cenicola for the New York Times
9 Oriental rugs layered in the J. Crew catalog, via Apartment Therapy
10 A zebra hide rug over an Oriental rug, via Sara Says Awesome.
Images as linked above