I usually practice in real quilts for charity. My Guild gives out the fabric already cut, batting, back and binding. You grab the bag, make the quilt, finish it and give it back. My quilting is not perfect but good enough to present the quilt to someone. I have improved my quilting skills and of course I do quilt the quilts I finish so I guess I also practice in my own real quilts!

Many quilt squares are 12 x 12, 18 x 18, 20 x 20 - just any size that it comfortable for you to use would be my suggestion. The 18 or 20 inch squares go together really fast for a nice big quilt.

Practice with QAYG squares and put them together at the end -- a charity quilt.

Use thrift store material and/or clothing.

I think maybe I'll do 16x16,... it would waste less fabric, and be a little bigger than the 12x12, which I find constricting. :)

Ah!! Or,.. duh. I could just piece the batting like was mentioned. Wow, I gotta sleep more often.

I think there's a chance rectangular would really over challenge a newb like me at this point (one very simple quilt under my belt, a few quilted projects, mostly FMQ practice... I spend -way- too much time fixing vintage machines, and not enough using them. :-/)

That should make a pretty quick QAYG quilt too, I would think?