After going through the stages of how to draw fashion sketches in 3 steps I’ve previously posted here and here, see some images that might help you as well: female plastic mannequins that you can find here. I’ve made some boards with the images and presented them below.
Each time you draw, imagine the red lines that describe the curves of the body: the lines of shoulders and hips. Also, if interested in more positions, all you will have to do is to flip horizontally the image.
For the images below, I did this for you, in order to study freely after them. But when you will dig for more positions, do this on your image editing program. Find some more positions online, by searching female plastic mannequins. After the exercise, please send me the drawings at firstname.lastname@example.org and I will reply to your questions. I will help you with some advice that is meant to improve your sketches. Good luck!