If you're just starting to quilt, choose a square ruler the size of the blocks you're cutting for your project. For example, if your pattern calls for 9-inch finished blocks, purchase a 9 1/2-inch square ruler for quilting. You'll need an extra 1/4-inch around the edge of the block for your seam allowance.
Square quilting rulers have a diagonal line that runs through their center. Following the diagonal helps you get a truer square when you're working with patchwork pieces.
Along with square quilting rulers, a novice should also invest in a long rectangle ruler, which is used for cutting narrow strips and borders. Long rulers are also good for squaring up your quilt edge before you bind it.