I made this rug last summer to be able to put legs on warm rug rather than cold floor while getting up in the morning. It is made from T-shirt yarn and I crocheted it with my fingers, because I haven't got such a big crochet hook.
I can recommend a very good tutorial for making really good T-shirt yarn - you can find it here. Unfortunately I've found it only after the rug was done and I can say that I've definitely missed few very useful tips.
Here is the list of main mistakes I did:
1. I did not stretch the yarn after cutting it. This is a really good practice, because you are getting more straight and homogeneous yarn. This also can help to hide cutting defects.
2. I used all the T-shirt including sleeves (greediness?), so my yarn had seams and thickenings. And it was a little bit hard to cut it of same width.
3. Using fingers to crochet. Well, it is fun to try crocheting with your fingers, but it's enough to do this once. Using a hook is much more comfortable, easy and fast.
Next time I'll take into account two of those. Anyway I'm quite satisfied of the rug I have. I looks a little bit messy, but cute at the same time.