I've just started trying to teach myself crochet too. I'm a VERY tight knitter, and usually have to go up quite a few needle sizes. (ex: I'm trying out the baby kimono from Mason Dixon, and I'm having to knit on a size 8 addi needle, because I knit so tighly.)
My first few attempts at crochet, I didn't have a curve, but my fabric had NO "give". I took it to an experienced crocheter and she said, try to go up a needle size. Well, I already had.
Right now I'm in the process of crocheting a baby blanket and I had to go up 3 needle sizes to get a fabric that had any give.