Dont worry. Best thing to do is to do it, make a bad attempt, and try it again at some point.
Geez! its so hard to work on new poses I swear. Once you see it comming out terribly, you just want to stop while you're behind. However, you have to tell yourself to keep going because you're secretly hoping that it will work out in the end. I have so many failed drawings it hurts.
Hey, I bought this book called Bridgman's Life Drawing when I went to a Community College for a spell. Its a Green Paperback and it helped me out with a few things. Some of Bridgman's work can be found actually by googling it.
Search it up and see If you can find out some stuff you've never knew before.