I'm very new to Toribash. I just got this game three days ago (5/27/12) and I just made this arm decap move just by randomly experimenting with my limbs.
I'm not gonna lie, it's not good, but the only way you'll get better is to continue experimenting.
Try to relax more, it looks better.
Here's a nice little tutorial, courtesy of Meamme0, I used to help me get better ~ Click me.