I found that it helped to practice on paper first. I just drew curvy lines over and over again. Then when I wanted to do something different like loops, I did that on paper. I had my students do the same thing and they all felt it helped to loosen them up and make them more receptive to moving the fabric under the needle in the same manner they moved their pencils. If I'm trying out a new design for the first time, I still do it on paper first, just to get the idea firmly fixed in my head, and then to my hand. Once you get an idea from your brain to your hands, it stays with you awhile.
Just relax and practice like everyone suggested. I like Suz's suggestion of meandering around a motif on the fabric. You can also draw lines on muslin and follow them. Much like doing it on paper, you'll get the idea in your mind and down to your hands. That will make transferring it to the machine a lot easier, even though you're reversing the process on the machine. You'll get used to that reverse "drawing" with practice.