As mentioned, get some old sheets or muslin and just go for it. You can do a practice piece, then put another piece of fabric on top and quilt it again. After I got the feel of how the machine moved, I got some large print fabric and practiced following the motifs. Cheater fabric would work well.
After I felt comfortable, I started quilting charity quilts for a local quilt group for more practice.
They always tell you to practice your quilting designs by drawing them first. I got a white board and put it on top of my frame, then practiced my design using my whole arm holding the pen, sort of mimic-ing the motion of using the machine. this helped too. Hang in there, and remember you are your own worst critic!!!!