I started out practicing on plain muslin sandwiches, but then started making placemats. I think they are great because the tension and seams are more realistic. Plus when you are done, you have something useful. I find that when I have practiced a little every day, the learning curve is much quicker than if you practice sporadically. I was doing great for a while, then didn't sew for over 6 months. When I sat down to FMQ again, it was like I was starting all over again.
I don't remember where I read it, but I did read somewhere that practicing one hour a day will really help you build your skills. In addition, have you seen the pre-printed "skillbuilder" tops that some vendors at quilt shows sell? They are pre-printed with lines that you can follow, all you do is make a sandwich and start stitching. I think Keepsake Quilting also sells them. I am very slow as I have to trace a design to follow, as I am trying to build muscle memory and I am not ready to jump into the "freehand" deep end.
Have fun and good luck!!!