I don’t think I can specify any steps other than capturing the proportions in an outline and filling in the shadows. Your ability and experience will determine the beauty of the drawing. Any posture can be artistic. However, some postures might be more sexy than others depending upon your intention to emphasize certain parts of the body as centers of interest.

Of course, you can take some ideas from sketching books available in book stores or online. But they won’t teach you anything valuable. Being able to copy a picture isn’t the same as sketching a model. Though, I personally can do both accurately. But, I never went to schools to learn drawing and painting. Only practicing can make the difference in your ability to put everything you see on paper. The best advice I can give you is to judge the resulting drawing and try to do it better next time. The style depends on your preference. If you are new to body anatomy, I advise you to start on fast 5 minutes sketches. Do hundreds of them. Once you understand the foreshortening effect, then start shading them with your best and careful touches that would take you an hour or two. This is how one hour sketch looks like in my hand.

And two hour sketches look like these in my hand.

You can see that the first one is practically a portrait with bare chest. On copying photos, I don’t have nudes (whole bodies) copied from photos, but I do have portraits done from photos (mostly movie stars).

So keep practicing doing 5 minutes sketches from life models and you will be fine.