Bring your needle and thread up at the start of your line, then down directly above to make a straight stitch. Bring your needle up an equal distance below the line and draw your thread through.

Take the needle under the straight stitch and over the end of your thread.

Draw the thread through and gently pull taut.

Take the needle back under the straight stitch at the top and over the end of thread again.

Draw the thread through, gently pull back on itself to tighten and then lay in the direction of your line.  This is your first stitch completed.

Take the needle down above and slightly further along the line (it should be level with the edge of your first stitch). Draw the thread through and bring the needle up and an equal distance directly below the line.

Take the needle through the new straight stitch and over the loop of the thread.

Draw the thread through and down.

Take the needle once more through the new straight stitch and over the loop of the thread.

Pull the thread through then back on itself to draw it taut, and finally back across in the direction of your line.

Work along your painted line using the same method, and secure the thread in the usual way.