Take your old T-Shirts and cut them into strips. The strips should be 1/2" to 1" in width. Once all the strips have been cut, tie them together. To opt out of tieing them all together and to save time; cut the strips, but leave one inch at the end and cut back in the opposite direction. Begin crocheting just like you would start a blanket.
If you don't know how to crochet, don't worry. You can knit or even weave the rug.
In this project I tied the pieces together, and did a single stitch crochet with a 6.00mm hook.