I belong to the School of Extreme Tension. Sometimes when I crochet with thread I end up with a painful gouge in my tensioning finger. This tends to created really crisp end products, but when it comes to garments, sometimes it's better to slow down, pay attention to each stitch, and just try to relax.
I started my socks over again this weekend, and I think I have it figured out now. Behold, the first attempt, alongside the second attempt. Same number of rows, same hook, very, very different tension.
I also discovered that a large bag of Chips Ahoys helps the relaxation process.