These products allow you to correctly line up and sew a straight diagonal line on your machine without needing to first mark the pieces, saving you time when making triangle-squares and Flying Geese units. 
diagonal seam tape

Diagonal Seam Tape

Skip drawing diagonal lines on fabric to make Flying Geese or triangle-squares. The tape sticks to your machine bed with the red line aligned with the needle placement. The black lines on each side are a perfect 1/4" seam allowance.

Editor's tip: You can make your own seam guide using masking tape you have on hand. Here's how!

Ideal Seam Guide

Ideal Seam Guide

Get accurate seams every time with a repositionable 10"-long seam guide. A notch allows it to work with wide feed dogs or a walking foot as well. Bonus: The rubber guide sticks to fabric, so you can use it to sew diagonal lines on triangle-squares without marking or to chain-piece easily.

Laser System

ViviLux 3-in-1 Rechargeable Laser System

Adhere a positionable laser light to your sewing machine and screw on one of three heads—crosshairs, line, or dot—to aid you in sewing straight lines, starting and stopping sewing at specific points, and sewing along a path for appliqué and machine quilting.

Editor's tip: Some sewing machines have a built-in laser guide. Check your manual if you're unsure.