Here are the ABC’s on your 8x10s, 9x14s, etc., for your Living Room that will help you get the size right.
Ideally, a rug extends beyond your furniture with the entirety of each piece sitting on the rug. But, it’s not a perfect world so there are alternatives that will work well.
If you can’t have the entire footprint of furniture on the rug, it can be a little smaller, but it should capture at least the front legs of your furniture.
But what if you have a dot of a rug that you love? A good option is to purchase a larger, plainer rug (like natural, jute, or natural colored wool) that accomplishes one of the two size options above. Then place the small rug in the middle. It has to be big enough to at least capture the coffee table with a couple feet to spare. The layered look is fun and makes great use of a rug that might not work elsewhere.