I use a drafting T-square for the final squaring. Also, 6 x 24, and the June Tailor rulers. Accurate cutting is also key. I have learned to square-up form the first piece of the block. I think squaring-up takes a lot of practice. I just have learned on my through trial and error. The T-square along with another ruler to make sure the corners square-up is the best to me. I'm sure everyone has there on ways of "squaring" a block or quilt.