I love the look of sashing and borders that are joined with an angled or "mitered" seam. The problem I have is sewing a straight line on the angle when joining the strips. I've tried marking it with a pencil but always seem to stretch the fabric with the pencil.
Today I found a good trick to solve this.
When I line up the seam under my pressor foot, I take a couple of stitches and leave the needle in the down position. Now, take a piece of folded paper and place the fold right up against the left side of the needle, it slides under the foot easily. Now move the bottom part of the paper until the fold is right where you want to end the seam. Stitch along the folded paper to make the seam. If you happen to make a stitch on the paper it doesn't matter because the paper rips out easily.
I used this for 5 " borders and it worked like a dream.