How should a staight seam usually be pressed?

A straight seam should usually be pressed with the seam allowances opened or to one side, depending on the pattern instructions and fabric type. Start by pressing the seam from the wrong side to flatten it, then press from the right side to ensure a crisp finish. Use steam to help set the seam, but be cautious with heat-sensitive fabrics. Always test on a scrap piece first to avoid any damage.