I love my 6 x 24 inch ruler. I use my 12.5 x 12.5 all the time for blocks. I also use 6.5 x 6.5 and 5.5 x 5.5 as well. I like the idea of practicing cutting on old sheets and table cloths from Goodwill. I haven't thought of that. If something is way off, I will fix it. But imperfections are part of quilting. Nobody is perfect. Just keep playing with rulers and fabric and you will gain experience and confidence. The first cut into fabric I really love is always the hardest, I find. Good Luck and keep trying!