For full bodies draw 2 centrr lines instead of 1 and both are curved. Make sure to mirror them against each other. Where they meet is the bottom of the pelvis.
The torso is (usally) a been shape. Once your happy with the general shape/angle add in the rib cage and other anchor points (e.g. hips, shoulders ect).
Build up the basic shapes before committing to detail.
That's how I usally do it