I second the suggestions to start with smaller practice sandwiches, and then work your way up to larger pieces slowly. Just the thought of learning to FMQ with a full size quilt gives me the shivers.
My other suggestion is to practice whatever design you are using by doodling first, over and over, on paper. I had heard this advice repeatedly, but always considered it to be a silly step....until I finally had to do it in a class...and wow! It really helps! Lots!