I think the charm of the running stitch rests in its simplicity. The thread is either behind the fabric or on top. It’s either showing or it’s not. It’s off or it’s on. I could write a Morse code message with ease. It’s a binary system in thread. Here is a group of simple ideas for where ever I need a line.
A few more experiments with lines
green running stitched and then with the green interlaced
The running stitch makes good hearts and tulips, too.
A few grids