Take a look at my examples and see if anything catches your eye.
You probably have some vines in your stash: what if you just quilted right on the edge of the pattern? Up one side and down the other: this gives you practice working both "forward" and "backward" which is helpful for improving your FMQ. Bonus: look how great the back looks!
Here I've got big circles that I just quilted like giant pebbles. If you're working with large circles like I do here, you'll get to practice making smooth sweeping movements and keeping your speed consistent as you go around a curve.
I chose this fabric because it had so many lines, I thought it would be great for eye hand coordination. With so many passes over the same area, you get a lot of FMQ practice in a small area! And what a great texture on the back!
Even simple wavy lines can be a source of practice: here the challenge is on keeping a consistent distance from the design you're following. This is great if you like to echo quilt (I'm looking at you, Appliqué Nation!). Now what if you made the wavy lines and then filled the empty space between them with pebbles or lazy eights?
Some fabrics will give you practice filling in a space. Here I used some Pearl Bracelet fabric and filled each bracelet with a spiral. Remember to leave yourself some space to get out of your spirals! To get to the next bracelet I just snuck out between two pearls and into the next one the same way.
Anything with large blocky areas can be used to practice space filling as well. You could try different designs in each distinct area or just work on getting your stitches consistent. In this sample, whenever I ended in a place that wasn't adjacent to where I wanted to stitch next, I just stitched right along the edge between the ares over to where I wanted to be. This is good practice for travel stitching!