I crocheted a rag rug using strips of old denim jeans. For this rug, I used a variety of jeans material, and different colors.
I used the pattern that is in this book: Not Your Mama's Crochet, by Amy Swenson.
This is the page, with the photo from the above book. Other than my jeans being more faded, it turned out pretty close to the one in the book.
Although, I was not impressed with the finished size (using the pattern), it was perfect to put in front of my bathtub. However, in the future, I will be adding more to the rug, by extending the rounds of the pattern.
Two tips: Cutting jeans is messy, and you will have bits of it all over as you cut and crochet. If you don't have any old jeans to cut up, you can find inexpensive denim clothing at thrift stores.
There are many crochet patterns in this book, including jewelry and a purse crocheted from recycled plastic shopping bags.