Practicing with muslin is the way I did it. I drew designs on it and tried to follow them and then also made large squares and circles and then tried to fill them with free motion meandering. I also drew lines the width of the fabric and then practiced doing C's and S's for the whole width of fabric. That s curve is used in alot of patterns as is the c. If following a pattern try not to look at the needle but ahead of where you are sewing or at a larger part of the pattern as you sew.
Freehand large circles are hard as are straight diagonal lines so don't worry about getting them right at first.
Practicing will also give you a chance to work on tension as you go. And most of all, don't grip the handles hard. Try to relax and use just fingers to move the machine.