Making t-shirts into yarn is quick and easy, and there is a good tutorial here. My t-shirts had quite large designs on the front, and the tutorial suggested not using that part of the t-shirt, but I thought that was a bit wasteful and used it anyway. The colours worked in well and the fabric tends to curl toward the design anyhow so it is not very apparent in the yarn.
I did try crochet but my big 4mm hook wasn't big enough, so I tried finger knitting and loved the easy no-tools method and quick results. There is a good tutorial here.