You may be laying down an area rug because you can t stand the color of the existing wall to wall carpet such as in a rental unit but trust us it will look much worse if you just throw down a rug.
How to lay an area rug over carpet.
Area rugs generally work best over short pile or looped carpet.
Rugs should always be anchored whether used on a hardwood floor or on top of carpet.
When laying the rug over carpet however the concern is more about the rug wrinkling or rippling which presents a big tripping hazard wrinkling will occur because as one area of the rug is stepped on it will shift assuming it is not properly.
Likewise if you have a plush style of carpet installed choosing a low profile berber or woven rug is your best bet.
The only difference when the rug is going to be used over a carpet is to make sure that the color of the rug complements the color of the carpet.