TEXTURE
You should aim to create a contrast wherever you can, including between your rug and carpet. The textures between the two should vary.
This arrangement works best if the carpet is low-pile or loop pile; avoid putting a rug over a shag carpet. The long length of the fibers will overwhelm the rug and make it appear buried.
A low-profile rug and carpet would work fine together, but a contrast creates a more exciting look. Consider fibers that add more nuance and depth like wool, especially if your carpet is nylon or polyester.
COLOUR
Even though you do not particularly like the color of the current carpet, you will have to put up with it because there is nothing you can do about it. Think about colors that go well with it to that aim.
There are numerous ways to experiment with color. To experiment with all your options, turn to the color wheel, the decorator's closest friend. You can choose a monochromatic appearance and add a rug that is the same color but maybe a tad darker. Add a contrasting due to your palette for added diversity.
The color you choose should match the look you wish to achieve for your home. Remember to take the rest of the room into account; it should affect your color decision.
SIZE
Your carpet won't look as though it organically belongs there if you cover it with an Area Rug that is the wrong size. For instance, a rug that is too small would feel haphazard and unanchored. People will be perplexed as to why a strange rug is strewn across your floor.
If it matches the arrangement of your furniture, a rug on carpet works best. Consider the size of the area you have picked. If more space is required, placing a few smaller rugs side by side will help.
