using a simple line or stroke to indicate detail really helps, especially in quicker drawings. For example using a line to indicate where the toes are on a foot rather than painstakingly drawing every little detail like the toenails. Even in longer poses the artist will use their judgement on which parts of the body they want to emphasize on, and like the previous posters were saying it's usually the bigger parts of the body, and important joints like the knees and elbows. As you continue lifedrawing you'll pick up on these things, I used to make the same mistakes but you'll learn from them!
"If you want to work on your art, work on your life" ~Chekhov