For basic rulers, I would recommend a 6" x 24" ruler and a 6" x 24" to begin. I use my 12 1/2" square ruler all the time to square up blocks, cut wider strips of fabric (example, when I am making 8 pointed star blocks, I will cut a strip of fabric 7" wide, then subcut the 6 1/2" squares from that for the number of blocks you are making, after cutting those, I cut 3 1/2" strips, as this saves fabric). I also use my 6 1/2" square ruler to square up smaller blocks. Those are the rulers I would recommend, as I use them repeatedly in my quilting. After that I would suggest buying rulers as you need them for your quilting.