Stem stitch is a favorite line stitch. It’s so basic and used everywhere. I like it better than back stitch because more thread is over the fabric than as in back stitch. It can also be used as a textured filling.
First step is to make a small stitch forward. Then bring up the needle up at the beginning of the previous stitch.
Then bring the needle down one full stitch forward, and bring up the needle up at the end of the first stitch.
Repeat, pick up a bit of fabric one stitch forward, using the previous stitch’s end point.
Continue making stitches in the same way.
Finish by bringing the needle down in the same hole as the end of the previous stitch.