I think the most important thing is to plan and know what you are doing; even if it doesn't turn out the way you like, it's better than drawing something for a reason you don't know (i.e. wrong anatomy because of reliance on references)

That's not to say you can't practice by copying others, but...just be careful. Seriously, start out with stick figures if you have to. It's more about the feel of the piece as a whole than how well you can replicate something.

some tutorials that helped me (read everything, it helps)
nocturnalpanda19.deviantart.com/favourites/49090637#/d41jp1v
deejuusan.deviantart.com/art/Resources-Chest-Back-FM1-281102292?q=favby%3Anocturnalpanda19%2F49090637&qo=4
turtle-arts.deviantart.com/art/Q-D-Anatomy-Lessons-Arms-and-Shoulders-292876095?q=favby%3Anocturnalpanda19%2F49090637&qo=3
shattered-earth.deviantart.com/art/The-BASICS-Using-References-255875213

I hear a good technique for improving your drawing skills is to practice drawing using only permanent ink so if you make a mistake you will learn to adjust your drawing to fit the mistake.