Palestrina stitch, which is also called old English knot, double knot stitch, and tied coral stitch, creates a line of raised knots that is useful for creating outlines and borders. The secret is to keep your knots evenly spaced and fairly close together. Here's how to do it:
Draw a straight line on your fabric to use as a guide in keeping your stitched line straight. Take a short straight stitch from top to bottom on the line. After pulling your thread through, come up again just to the left of the bottom.