From McCall’s Sewing in Colour
When sewing a seam in garment construction, first match all notches or tailors tacks then pin at a right angle to the seam as illustrated above. This will mean that when sewing, the machine will stitch straight over the pins.
This is an especially neat trick when sewing more complicated, or curved seams as the pins will hold everything in place as you sew. Try to use the thinnest pins possible so as not to damage your fabric, & to ensure the machine does not get caught up on the pins.