You are off and running with your free-motion quilting...congrats!
I liked practicing on a Panel. You can outline the shapes in the panel or do an all over design, like loops (cursive L).
Having a larger practice piece helped me learn to move the quilt sandwich and get use to the moving the fabric to the speed of the needle going up and down. Also, put on music or podcast you like as you practice as it may help you relax. Have fun!